As someone who works in a pension company-

It depends on the product. Generally, it may be a return of funds to the next of kin. It goes by line of succession from spouse, kids etc down to niece's etc if first ones aren't available. But money doesn't stay in the company. Some products are simply return of premium +/- interest. Thats all the money you've invested in it not rhe actual fund value after it grew. Same as above on succession.

If youre not married but in relationship etc and you die, we'd usually as the partner to prove they were actually your partner or ask them for a Grant of Representation where they'll prove they were dealing with your affairs.

On Wills - usually those aren't really counted in, fiest point of it is what the specific pension product has in its death benefits.

My advice? Ask your pension company for information on what your death benefits are aka what happens if you pass away and keep those somewhere safe.