I'm sure that Merlin have thought about this and taken necessary steps; they don't want to spread this virus, and they don't want to make the situation any worse. They care about their employees and guests; the park is in the very business of giving people fun and enjoyable days out, so spreading a deadly virus negates the point of the park's existence. They will take the necessary precautions, and I'm sure they will open in the safest way possible.
I'm sure everything will be fine for those who want to visit, and the park is perfectly safe to be in, but I'm not personally sure that I want to disobey the government's current advice on mass gatherings. As much as I hate to admit it, theme parks certainly aren't essential travel at the moment. I don't want to risk giving the virus to someone vulnerable, whether they're in my family or a complete stranger to me. The rides will still be there for me to ride once all of this has blown over, and I should hopefully still have a Premium Merlin Pass (as far as I know, it's valid until February 2021). People are free to make their own choices with regards to what they do, and I have full respect for anyone who does visit, but I personally don't think I will be visiting next weekend (when I was originally due to go).