No, it's not time to say goodbye to Mario.
the guy is extremely talented, and still young. We should stand by him and let him mature and develop, on and off the pitch.
With that said, he does hurt the team a lot of times with his antics (much more often than he should). I love the guy for his confidence and lack of fear for the extraordinary, but he does need to calm it down so that the team doesn't get hurt (red cards, workrate at times, and so on).
If it was up to me, this is what I'd do for our striker rotation:
Aguero and Dzeko would start together as often as possible. They complement each other nicely, and their goal tally is excellent. I think highly of both players, Aguero no need to say anything really, he's a star who has a great understanding with Silva (though he has gone now a few games without scoring, hopefully he can snap that streak soon) and Dzeko hasn't been consistent, but he is very unique in that he's big and strong (only striker in the squad who's really good in the air as well) and plays for the team at all times. Balotelli would be my #3, not because he's less talented than Dzeko (actually I think he's a bigger talent than Edin) but because as I stated earlier, he does stupid things on and off the pitch where you just can't rely on him as a starter, there is just no way we can do that until he matures. No way.
Then, I'd find a #4 striker who's willing to be #4, but knowing that Balotelli is always going to miss some games bc of who he is. So really, whoever we get at #4, he'd almost share #3 with Balotelli by default.
Tevez, I wouldn't consider.