The main risk I can see to Scarefest from covid-19 is a decrease in attendance as anyone in an area placed in Tier 3 rules should not be leaving their area. Manchester & Liverpool are a huge conurbation about an hours drive away.
I guess indoor attractions are also at risk of being closed - so bye bye to the 3 mazes, Hex, Duel & Sharkbait Reef. On the flip side, I would argue that there are just as many touch-points on outdoor rides / their queues - where the ride station is generally indoors or at least undercover.
The worst case scenario is obviously that parks are forced to close... it's a bit of a waiting game really until Boris speaks later today.
I for one am giving parks a miss this year. I know how to socially distance, but it is clear that some guests don't. Nemesis will still be there in 2021.