I've tried a few times, but other than collectors in Dau that eventually all run off, I've never managed to do it. Anywhere there are Assault-type bots, more just keep jumping in as the old ones die off. I assume that were I to succeed, they'd all be back the moment I jumped away?

Yes they’ll keep on coming back after some time. The longest they’ll be away would be in dynamic hive skirmishes.

Yes it is. Youll get a sector chat and then more bots come in.