I left him unrescued in 1-1. I killed Phalanx, then went to the Nexus. Reentered 1-1, killed Ostrava and went to the Nexus again, and Ostrava was sitting there (I had not gone into 1-2 yet, he would have reappeared there if I had). I didn't even have to talk to the Maiden in Black or the Monumental. He appeared in 1-2 as well when I got there. After this he should pop up in his usual places throughout world 1, and he'll drop yet another Mausoleum Key in 1-4, or when killed.
So you have to go by the Nexus after killing Phalanx, then by the Nexus again after killing Ostrava, before he reappears/revives. It also looks like he must be rescued and give the Brass Telescope gift before he dies, for the bug to occur.
- I have also killed him in 1-1 after defeating Tower Knight, and once after beating Penetratror, and he was in 1-2 both times.
- I have also tried before killing Phalanx, but couldn't get him to reappear in 1-2.
- I killed Phalanx, then went to the Nexus. Reentered, killed Ostrava and went straight to where he appears in 1-2, but he wasn't there.
- I killed Phalanx, then Ostrava, and went to the Nexus. Reentered in 1-2, but he wasn't there.
- Also, all of Patches' unlockable items should be available when Ostrava dies the second time.