Well, some people asked me to post this in order for it to be saved here, so here's my method for Fe5 style escape chapters with no ASM required.
I have an conditional ID for each of the character outside of Leif himself, in the AREA event of the escape tile I use use IFs to know the character ids, and for example Olwen is the one escaping, I trigger her corresponding conditional ID. Once Leif escapes I check if the condional IDs of the characters are active or not, if they are, good, if not, they are simply released from memory.
If later on I decide to implement a "get them back" chapter(the one in Thracia were your captured units could be gotten back) I can instead use Permanent Conditional IDs that will carry over to all the game and later on check for which units were captured.
Here you are, the method is quite simply, it's only boring to make conditionals for all characters.
Have fun with making different chapter goals now.