I'd imagine that Tails was off doing something of his own accord to help out from a distance while Sonic and Chip took care of the planet. Seemed to make sense to me. As I said, if the focus wasn't on the main conflict then we'd probably never see them apart. Like when things were resolved at the end of SU and the two of them were running and flying along beside each other going who knows where (a bite to eat perhaps?)
 |  |  |  |
