At this very moment, I chose to enter a gate and join a random party, the party leader is very much AFK and its been five minutes. Seems kind of unfair that leave party or joining another party (for 10 more energy) are my only options, it cost me 10 energy to get here.
I think if you want to leave a party and go solo, you should be able to any time. Though I recognize this could affect things from a coding standpoint. If this could be implemented, this would be great.
A form of this already exists at the tier 1 to tier 2 crossover (and I'd assume the same is true for the tier 2 to 3).