Female vocalist is a genius move for avoiding comparison.
Just hope they find someone with a unique tone/timbre, not the generic pop female singer like that Sydney Sierota from the Hollywood Bowl. Wasn't bad, but far from anything especial. Over the last few years the only female vocalist i would call outstanding is Courtney from Spiritbox. That's a one in a million voice.
Bonnie really did surprise me in the Bleed it Out video, and it was the test i needed to accept LP with a female singer. It can happen and it can be very good!
Can't picture them going with a novice singer, not well known or already being part of a relevant band. It's a tough job not only in a singing level, but in a interview/media level, in a stage presence level, in dealing with expectations level... that's a tough responsability, and it takes experience to deal with that.
About Rob, not really a surprise. It's sad but understandable. I could see him featuring in one or two songs in concerts near his home or something like that. Frank Zummo is the call, he was amazing in the Hollywood Bowl and very respectful for Rob's parts.
Regarding Joe, let's see. This was the biggest surprise so far. Thinking replacements, Jordan Fish came to mind, but he's too similar too Mike in the production level and it could get a little bit weird.