I could find two "evidences" for it. And I'll admit none of those are especially strong but I'm throwing them anyway. The wiki points out that there is no specialized counter spell, but that doesn't mean the charm can't be broken by force or by "wrestling" it.
First one is that the Weasley twins joked about sticking Ron's badge to his forehead. While their sense of humor can be somewhat extreme at times, I find it funny that'd they'd joke about a truly permanent charm. But as the wiki points out, it's never said if the spell can be circumvented by simply removing part of the surface it's cast on (which would be ron's skin).
On a more general level, I don't remember any spell/enchantment that can't be reversed, cancelled or at least affected by the caster. As such, my guess is that it an be reversed.
Note : the following paragraph is mostly guesswork
Now we have examples of portraits like Sirius' mother resisting many wizards (Sirius amongst them) for a long time. And Sirius' pictures resisting his mother for a long time too. What that tells me is that even if Sirius' mother is the most powerful wizard of the two, she couldn't break it and Dumbledore probably tried to break it. None of those worked. What that tells me is that it's probably removable, but akin to an encrypted communication. The remover need to have precise knowledge of the way the spell was cast (or have a mental fingerprint of the caster) to realistically break it.
