I left my state employee money in their plan just so I can access the state employees' healthcare plan in 20 years!
Pensions tend to be insured these days . . . I don't think you should worry too much about it disappearing. You can always look into that, but the govt nipped pension raiding in the bud through legislation.
I did a series of calculations on the pension payout they were trying to give me last year, and I'd have to realize 7% actual returns every single year from now until retirement just to break even. No, thank you, I've got plenty of other money in the market and I'll keep that defined benefit pension intact for grocery money for guaranteed old-lady me; there is a 5 year payout to my heirs if I die which pretty much adds up to the amount they were trying to give me now. So, I figure if I die unexpectedly, the kids will get the payout they offered me anyway, and if I live to be feeble and old, I'll end up way ahead. But I am vested (they changed the vesting rules dramatically since I vested, but I am grandfathered in.)
Your situation might be different, but I think you really owe it to yourself to run the numbers on what the pension would actually be worth if you do vest at some future date. Taking the money now for a house could be a great idea, or it could be very short sighted.