The fund managers will do their best to manage the risk but it will never be 100%. TheBrit thinks this is box standard risk under LDI and no need to overworry about one off freak market movements. Apparently there are 10-20 other ppl who share his views and currently running your pension fund. I think different and seriously begging ppl not to let them do more of this with your money. The risk is not as remote as it sounds, it happened in 2008, every now and then for the random fund and it just happened last week.
Perfectly healthy and solvent funds have gone under in hours because they could not find liquidity quick enough to absorb market movements. When they firesale assets under margin call, these are sold in big amounts asap to then highest avail bidders. Traders and normal investors make their own guesses to try and profit from the market and when they see block sales like that, they might guess there is a margin call on a position. Gilts that are known to be held mostly by pension funds? Maybe it's a good time to short the pound because I think it'll drop soon. It is market risk they cannot manage no matter what they do.