I thought that at some point I had read something like "if you pass you PS to a ship using swarm tactics and the ship that did the passing dies, the ship that had the higher PS passed to it no longer gets the bonus.

Example: Howlrunner uses her swarm tactics to pass PS 8 to an academy pilot. She then gets killed by Wedge. Does the academy pilot still keep PS 8 for that round of shooting or does it immediately drop back down to PS 1?

I tried to find whatever it was that I had read, but I can't find it. Any help would be awesome and thanks in advance.

No it doesn't suddenly drop back to 1 just because Howlrunner bit the big one. The card states it lasts until the end of the combat phase. It will drop back to 1 at the beginning of the next turn.

I have a related question. If you have Howlrunner and some Black Squadron TIEs, and they all have Swarm Tactics, can they all pass around the PS 8 from Howlrunner? For example, Howlrunner to a Black to another Black to another Black until they are all PS 8?

It's a chain reaction, and a quite valid use of the upgrade. Your only restriction is making sure they're all close enough to pass it on to the next ship in the chain. This very scenario is used as an explanation in the FAQ. This is also what can make a TIE Swarm very deadly.