In 4vs4 games, if someone in your team quits with no explanation, especially in the first 15 minutes with no fighting, what do you think the other team should do?
There are cases where the player quits almost 1h after fighting, in imperial etc, where he can’t fight anymore. Not the case I want to cover here.
The 3 in a team should surrender
You cant let your guard down. 3 can still defeat 4 if they are better players and/or have better civs
Interesting. I would obviously surrender for pratical reasons… It’s idiot to fight in almost every one of those cases.
Technically it can be done if the quit is on start, but chances are still small… But after 15 min, entering mid game it generally screws up every time.
Depends on map and players/civs. If you and your friends are high 1v1, but play just a few TG from time to time, it’s possible that you are more skilled than your opponents, for example, so a 3v4 is possible even after 15 minutes.
Of course it’s possible. Just like an 800 elo can beat a 1200 elo
It simply more likely means match making has failed if the chance is probable
Maybe, only maybe, you have missed this part 
Now that I kindly pointed it out to you, you could read again to see how it’s not a matchmaking problem.
It’s possible also that your team gamble an all-in and emerge victorious. A drop or rage quit doesnt mean, necessarily, end game for a team.