Please arenanet, this should be fixed.
A simple debuff(not allowed to tpvp for said amount of time) might fix the problem.
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or
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This is how most games do it, if not everyone readies by said time, you don’t start the game and whoever didn’t get kicked out of the matchmaking and the party remains. (this is before being put in the match)
Of course if its a premade they can easily re-do the party by quitting it and getting everyone back together, or even just inviting that one person back.