Check the Victory status tab in the Cilivilisation Manager.  It'll probably say the same thing, but suffice to say, if the Yor are still hanging onto their Ascension crystal, then because of the headstart they have they can still win.  If they can't make any progress at all then they can't win that way.

Pirates suck, I know.

I am afraid that the only way to stop the Yor from ascending is to smash the base.

Luck for you, attempting to ascend in anyway will piss off everybody else, so some AIs might gang up on the Yor.

Losing by Ascension is generally not an issue as it takes forever to ascend, even when the enemy AI has all five crystals (200 weeks of King of the Hill, almost 5 gameyears, seriously, if any race can hold all 5 crystals for all that time, they deserve the win.).

Also it doesn't really matter that much if you blow up their base 400 weeks before they ascend, or just 20 weeks, getting closer to ascension offers no bonus whatsoever and it annoys other AI...

Ascension works through collecting ascension points. Each turn you hold one ascension crystal, gives one point. If I recall correctly, you need (the insane) 1000 points to actually win. That means that if you have one crystal, you need to wait 1000 turns ("weeks") before your ascension is complete. If you hold two, you "only" need 500 turns. If you hold all 5, it still takes 200 turns to win the game through ascension. So basically, the Iconians may have gotten a crystal first, but because the Drengin have gotten themselves two, they will still finish ahead of the Iconians, even though they may have fewer points right now.

Ascension really isn't a problem though. As I said before, even when holding all 5 crystals, it takes a whopping 200 turns. If a race is strong enough to hold all 5 bases for 200 turns in a row, it might aswell have gone for a conquest victory (it would've been won much easier).