Potential AFK/Disconnect solution/workaround.

So I'm just coming from losing a game due to our pathfinder being afk. There was quite a while where he was afk and my other teammate was downed and later dead. 

So my suggestion is this:

Measure input. 

As long as there is input all is fine and the player is active. But as soon as it stops, a timer starts and after a while an option to take over that player is available for dead players. If the original player comes back, the control is returned to that player.

So lets say player 2 is downed while player 3 is afk/disconnected (but still in the game). Player 1 can't revive because there are enemies nearby. Player 2 dies, and player 3 is still afk.
Player 1 then picks up player 2's reboot card.

Now player 2 can choose to take over player 3, but you still have the option to bring back player 2's original legend and swap back. 

If you swap back, player 3, if still afk is left to stand where ever they are when the swap occurs.

If player 3 returns at any point, control of their legend is brought back.

This might not be perfect, but at least it could save you from some annoying deaths.

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2:

One could also potentially use a system where people who start with a team that isn't full get reinforcements when other teams get killed.
Option to join late toggle in menu. Some badges and a bit of gear on drop would also help. Maybe like in control with some options to choose from.