Toxic... Lunatic. Semantics...
Jones isn't toxic as far as we know, so there's no point to fire him in that case.
I'm not sure you can just "save" money by not paying bonus tied wages upon firing. Regardless, I imagine there's very few bonusses he'd be getting if he's injured and barely plays anyway...
If he decides to mutually end his contract so he can move on a free or if we manage to sell him on a for a small fee you might end up making a loss, which again, why risk it if Jones isn't being a nuisance.
And all this is under the assumption that you know he's going to be near useless while he's carrying the injury, which is just talking in hindsight.
Basically you're talking about this stuff in a generic sense when that's completely pointless 'cause we know who the subject is.
And btw, Van Ginkel at Chelsea had a similar disastrous injury spells at Chelsea and was given a one year extension after his contract had run out. So this idea that having an injured player on the books or something is "exemplary of the current state of Man Utd", which I've seen mentioned a lot here in this thread, is silly.