You cannot put HDDs on different consoles in no way, even if you replace the motherboard which would be the best case scenario to rescue the dead PS3 you would need to format your HDD.
Answers to your questions:
1. Depends on the game. Some do, some not.
2. If the game allows that, most do, but there are a couple who don't since their developers don't care how cloud gaming works or there isnt any patch that allows you to use cloud savegames as your own savegames and not get treated as USB copied savegames.
A. No, since you won't be able to reach that step at all because of what I said above.
B. You cannot remarry HDDs in any way. Especially hardware from different SKUs which store on the HDD important files specific for each hardware revision.
There are 3 things you can do.
1. Insist trying to rescue the PS3.
2. Reallise that the PS3 is dead and took on it's grave together your savegames aswell and get over it.
3. Wait for a very (unprobable) fix on breaking the PFS hdd file system, which wouldn't importantly offer you that option nor after so long that it would get released it would be that worth of waiting.
...and the worlds shall reconnect