There are a couple of possible things at play here. First, is he wearing a pull-up or something at night, or just underwear? The reason I ask is that if all the sheets and such need to be changed before he can return to bed, he may just honestly be fully awake and can't fall asleep again. Nightime pull-ups until no accidents for 3+ months should do the trick. If that is not the issue than he is just being stubborn.
Talk to him during the day about what is expected if he wets in the night. If he is uncomfortable he can change his pull-up or whatever (at 4 he should be able to do this quietly by himself) and get right back in bed. That's the deal. If he cries and throws a fit there will be consequences. Make sure he knows the issue is not the wetting. Wetting is no biggie at all, but throwing a temper tantrum about following the rules is a big deal. The rule is we all sleep quietly in our beds until morning. If you disobey that rule you will not be happy. Figure out what the consequences will be ahead of time and let him know in advance. 'Tonight if you have an accident and don't get right back in bed after you clean up X will happen.' (since what he wants is tv, taking away tv for the next day is a good option) I would also have more consequences if he escalates the behavior. 'If you don't go right back to bed you lose tv for the next day, and if you cry and wake up your sister you will will also lose dessert (or a play date, or video game if he has them, or whatever). He needs to know that he is responsible for his behavior and that if his behavior makes life difficult for other family members he will have difficulties of his own. :o) At four years old he is fully aware of obey/disobey and is making choices about which he wants to do. As parents we have to do our best to make that an easy decision! I always tell my girls that I can't make them obey, I can just make them the saddest girls in town when they don't. :o)
Good luck on your continuing adventure in parenting!