We don't know, that version of Sanctuary II is never seen again after Nebula leaves and we don't see Thanos go back there. However, we know that Thanos wasn't wearing his armour during the events of Avengers: Infinity War after attacking the Statesman, for example, when he completes the Infinity Gauntlet.
He leaves that armour on the Statesman but at the end of the film and in Avengers: Endgame we see his armour hanging up in the Garden.
This is unlikely to be the armour he was wearing at the beginning of Avengers: Infinity War as that was most likely destroyed when Thanos used the Power Stone to destroy the Statesman. We could argue it got transported back to Sanctuary II as well. If so it never leaves again. So it's possible before going to the Garden Thanos went back to his ship picked up a few things, including his armour and then left again. As it isn't seen at the Garden though we know he didn't take it with him.
It stands to reason that if Thanos does go back to Sanctuary II before the Garden he told the Chitauri manning it to go on their own way. If not they would've realised Thanos had completed his plan because half of them were likely Snapped and so likely went their own way after that. So, it's unlikely to be floating in space free for the pickings but we don't know exactly what has become of it because there's no information on it after Nebula escapes.