Players connot join the party while you are engaged in combat

[Amineri]

I agree. Most of the heatedness that I've seen so far has been from two sides:

Side A : I keep getting DCed and dropped from my party, and can't get re-invited. Please fix.
Side B : Inviting party members during combat is terribly exploitable. Don't add it.

Looking at the problem (side A), there are the three parts (1) getting DCed (2) getting dropped (3) unable to invite in combat.
Many people have suggested fixing (1), but there are simply too many variables for that to be a reliable enough solution. I see many people suggesting changing (3), but it does seem horribly exploitable, and the devs have pretty much come out and said that there is no plan to change this.

This really only leaves (2) as a viable way to fix the problem. Keep party members who disconnect from leaving the party. Even this is open to certain degrees of exploits, but game design (and life) is about a series of compromises.

My 2¢

@everyone in general;
In short, address the specific, crippling issues, without negating the actual needed limiters.