What happened to the Imperial Star Destroyers after the fall of the Empire?

Question

There were approximately 25,000 Star Destroyers (mostly Imperial-class and Victory-class) in service of the Empire at one time. Only about 50 of them participated in the Empire's two biggest defeats (the Battle of Endor and the Battle of Jakku), so the vast majority of them were still operational when the Empire capitulated and signed the Galactic Concordance. Indeed, under the terms of the Empire's surrender the Imperial Navy was allowed to continue operating within the borders of the territory controlled by the Imperial remnant. In the ensuing cold war between the Imperial remnant and the New Republic, hard-line Imperials retreated from the Imperial territory in the Core and Inner Rim and retreated into the Unknown Regions to form the First Order.

What happened to the tens of the thousands of Imperial Star Destroyers of the old Imperial Navy during the cold war and rise of the First Order? I would imagine that many of them would remain in the Core and Inner Rim with the part of the Imperial remnant that complied with the Galactic Concordance, but the hard-liners who formed the First Order probably took quite a few of them as well. The First Order seems to mostly use Resurgent-class Star Destroyers, which are designed from but considerably larger than the Imperial-class Star Destroyer. Did the First Order construct Resurgent-class Star Destroyers out of the hulls of their Imperial-class Star Destroyers or do they still have all the Imperial-class Star Destroyers they took with them when they retreated to the Unknown Regions?

I'm looking for rough percentages of each of the possible fates of the Star Destroyers backed by canon sources: x% were destroyed, y% remained with the compliant Imperial remnant in the Core and Inner Rim, z% were taken by the First Order, etc.

Answer 1

In smaller battles after the Battle of Endor, many Star Destroyers were lost or surrendered to the New Republic.

According to Wookieepedia, this was due to a lack of resources:

With most of the Empire's veteran troops killed on the second Death Star or Vader's command ship Executor, military paucity and tactical clumsiness soon hampered the Empire's efforts at a concerted strike against the Republic. The Imperial Military suffered numerous losses of warships and troops, and expended more ordinance than it could produce fighting Republic forces. This ultimately led to a supply deficit forcing Imperial-class Star Destroyers to make do with an inadequate supply of TIE/LN starfighters and resulted in both the Imperial Navy and Imperial Army utilizing undertrained personnel pulled early from the numerous Imperial academies. Consequently, many planets were either captured by or seceded to the New Republic.

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The majority of captured Star Destroyers were eventually retired by the New Republic as part of the Military Disarmament Act.

The few that remained were most likely stationed in the Hosnian system when it was destroyed by Starkiller Base.

According to Wookieepedia:

The Military Disarmament Act was legislation aimed at legitimizing the transition of the Alliance to Restore the Republic from a military resistance movement into a democratic New Republic by significantly reducing the size and scope of its centralized defense forces. The initial proposal called for a ninety percent reduction of the New Republic military, which then consisted of a starfleet, a ground-based combat army, and a Special Forces division. While the remaining ten percent would be retained for small-scale defense efforts, all other military investments were to be diverted to training the local armed forces of Republic member worlds. The provisions of the act would only be implemented after the official end of the Galactic Civil War between the Republic and the Galactic Empire.

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Most of the remaining Star Destroyers were wiped out at the Battle of Jakku, with only a few surviving (and eventually becoming the First Order).

After a series of lost battles, the Empire brought their remainin Star Destroyers to Jakku to join a force called the "Imperial Remnant", under command of "Counselor to the Empire" Gallius Rax. These forces were almost entirely wiped out by the New Republic (and Gallius Rax was killed). The few remaining ships, following a final order from Rax, escaped to the Unknown Regions to begin forming the First Order.

Answer 2

They were probably scrapped for lack of funding.

Large fleets require lot of resources to operate. There is one mitigating factor, economy of scale, when you have lots of certain type of ships it is cheaper to produce them and maintain them than when you have only few of them (cost per unit of course). Empire breaking up is somewhat similar to breakup of Soviet Union. Although successor states inherited Soviet military hardware, their combined financial might was not enough to maintain all of those. Even biggest successor state (Russia) didn't keep all of ships, subs, planes and tanks it inherited. Instead, Russia chose to use or mothball only best parts of weapons it had. Rest was either sold or retired and ended up scrapped. Smaller states kept even less part of hardware they inherited. In SW universe, there were even less potential buyers for Star Destroyers. Therefore, it is easy to imagine that various Imperial factions, that suddenly didn't have central government to dole out cash, simply got rid of military surplus in one way or another. Of course, biggest of them (First Order) similar to Russia in real world kept most promising designs and upgraded them. But even First Order didn't bother with obsolete and useless ships.

Answer 3

They were probably destroyed and crash landed on other planets. You see Rey in one on the Force Awakens. There were a lot of them on the one planet.