Should the Pkunk rejoin the Yehat?

At some point in the game the Pkunk decide to rejoin their relatives, the Yehat. You can easily enough convince them to forgo their plan and go back to their home world.

What are the consequences if they rejoin?
What are the consequences if they don't?

Solution 1:

SPOILER WARNING IN EFFECT FOR ENTIRE ANSWER

Given the nature of the question, it really can't be any other way.

First,

You actually can only convince them to turn back twice. Each time you use an argument they find persuasive that answer won't be available the next time they decide it's time to reunite. The third time, you're out of arguments that they'll accept and cheerfully fly off toward their destiny.

This is important, because

If the Pkunk attempt to reunite with the Yehat before you start a civil war by showing them the Shofixti are still around, the Yehat will absorb the Pkunk and you'll never hear of them again.

However,

if you start the revolution first, and then let the Pkunk reunite with their Yehat brethren, the revolution will end victoriously -- and when you're about to depart on your final assault against the Ur-Quan dreadnought, you'll be approached by a party of combined Pkunk and Yehat ships; the Yehat are now ruled by a Pkunk queen, and they'll be assisting their cousins in reaching enlightenment and happiness and transcendence. Oh, and they think you're about to get yourself into no ends of trouble so here's a dozen ships to help you out...

Solution 2:

While another answer covered the short-term consequences, it had the wrong long term consequence.

If the Pkunk attempt to reunite with the Yehat before you start a civil war by showing them the Shofixti are still around, the Yehat will absorb the Pkunk and you'll never hear of them again.

As covered in the answer to this question of mine: Is there any downside/difference to Pkunk being absorbed by Yehat? (sorry, I asked it without noticing this question):

It does not matter in the end if Pkunk are absorbed by Yehat! You will see their ships in the battle against Sumatra regardless!