How common are group lift-outs in ER, where team goes to new bank?

Hi, working for a senior Analyst at a BB in NYC. Ever since bonus time a few weeks ago it seems clear my Analyst is planning to leave the bank. Trying to anyway. He specifically invite me to come with him to the new bank, but I'm just wondering what are the chances of this happening and what are the chances he leaves without me (we have two Associates on the team)? I really enjoy my sector and my mid range goal is to launch coverage on a few smaller names in the sector. Should I be worried if we go to a non-BB, or is the Analyst name the most important thing to consider?

Also, Is it possible to transition to a different BB working for the same sector... or is this a very low likelihood event? Should I be looking at new firms, to protect myself?

I'm a gold star contributer, but this is a pretty sensitive topic and I'm trying to be discreet. Thanks guys and I'm looking for input from those of you who have been in this situation in the past.