Cavani, even in his latter years, isn't someone I'd see as a punt, in that his wages are rightly exorbitant and you would be expecting premium performance out of him to justify the cost.
If you are going to pay top dollar, you have to have everything in place to make use of your asset otherwise, why not just go for a cheaper option who is more of a punt and won't be one of the highest paid players in the entire squad?
Cavani, along with Ronaldo, are still in what should be considered, a league of their own when it comes to off the ball movement and it would be bonkers of us to get him in and then have next to no means of supplying his movement with the passes it warrants.
A fit Pogba and reliable Mata, and this kind of signing would have justification; Cavani would surely be a tutor to all our forwards on how to move, which could benefit them for the the rest of their careers, being one extraneous benefit outside of his expected goal return and decoy value.
I don't think we'd look to buy him prior to a loan, personally. It'd be a case of seeing how his body holds up in a far more demanding league, but even a loan for this tier of player will come with a fee and very probably a premium wage that could be better used elsewhere if we're not going to meet the aforementioned prerequisites to optimise his skillset.