I would not think he would be very healthy even though he got out of the trap. As mentioned above it is pretty much guaranteed that he is not the only rat, a pair can multiply into many in a short time. Here on the farm I am in constant battle with rats, mice and chipmunks 365 days out of the year, animal feed draws them in like a magnet so it is never ending.
I use every tool there is to control them and keep numbers very low, traps, water bucket traps, poison, guns and dogs.
Al