sealing the room has a high failure cost. if he manages to get out before the door shuts he has all the time it takes for us to un-seal it to build a lead before we can try anything else.
Depends on how long it takes to unseal it. Could be a complex spell. Could be that the actual sealer of the room can unseal the room with a simple thought. We don't even know yet HOW the room is sealed (locked?, magic barriers?, anti-apparition?, what?).
This is one of the answers we are waiting for from the GM, and why many have stated they might change their votes in response.
Keep in mind, guys, that the important thing was that we outed the rat. If I recall, the rat didn't flee until we specifically talked about it being evil, and suspecting it. That means it understood us far better than any normal rat could. Therefore, we have evidence that the rat is more than it seems. Plus, the detect evil spell pointed out Draco as evil, so it can't be wrong, can it?
This is all we really need out of this encounter, so chasing him to Antarctica and back isn't worth it.
All this will tell us is that Ron had an evil Rat named Wormtail (a name that only Remus Lupin will recognize, and we have absolutely no way reason to tell him). Further, if he runs away in his rat form, we will have no proof, and will just come off looking like a lunatic to everyone but Moody.
However, if we were to say chase him out and as result force him to turn human in order to apparate away, we would atleast get a chance to use Mage Sight on him in human form, which would likely show not Wormtail but Pettigrew. And Moody WOULD recognize that name.
Basically, I see this going 3 basic ways:
Best: We capture Pettigrew and force him into human form infront of multiple witnesses, then manipulate our reputation to get Sirius out.
Bad, but salvagable: Pettigrew escapes us, but we learn who he is. This gives us IC reason to investigate Pettigrew, which will allow Harry to discover Sirius, the fact Sirius had no trial, the fact that Pettigrew (a man supposed to be a hero and dead) is evil and running around as a rat, etc. Harry will have no proof of anything, but HE will know.
Total failure: Pettigrew escapes into the woods without being exposed. Harry knows there is an evil rat named Wormtail out there, which for all intents and purposes is utterly and completely useless.