If he's available we should consider it to be honest.
I agree with those that say we shouldn't break up the Gerrard - Torres partnership, but the fact is that they have actually only started 13 Premiership games together this season. Torres' hamstring problems are well documented and Gerrard is picking up more niggling injuries as he approaches 30, so I don't think lack of game time would be a problem for Tevez. He's best suited to play off a target man, but he is versatile enough to play with Gerrard up top too - United won the league playing Tevez/Rooney up top last season and neither was a 'lead the line' type of striker.
I wouldn't pay the 30 mil to sign him outright, but a similar loan deal to what United had him on would be a decent plan imo.