Collection of solutions for rambo cav:
1. Make the captain do no damage when too far from his squad (like in Warband custom games and NW)
2. Have all captains have something along the line of 1-3 respawns. As an infantry captain, if you die in an engagement, a lot of your troops probably will too, so it won't be such a change. As archers you just have to be a bit more careful (balanced with having cav rambo less), as cav this will fix that dumb s*** called ramboing.
3. New suggestion, (might make a thread about it) unit morale: Each time the captain dies, a % of your starting troops start running away (like in SP) and desert your unit. Increasing with every time you die. I would say about 20% of starting troops running away would be a good idea. That would mean about 3 when dying as heavy infantry, 5 when talking about peasants and 2 when it's heavy cavalry like knights and cataphracts. Also makes sense for more "professional" troops to have less soldiers leaving at a time than say, peasants, but not the point though.
4. Force the bots to follow the captain when left too far behind (not desireable and would probably still not fix the problem).
I would honestly like the idea of having 2. and 3. combined.