Wasn't that the plan all along anyway, though, however problematic? The plan was to escape to the future to avoid being found by Leland. Leaving him behind makes him Starfleet's problem. It would've made more sense if they threw HIM into the future rather than the sphere data.
No, leaving proto-genocidal AI behind to turn eventually into Nomad in 500 years was not the plan. In fact that is the opposite of the plan.
or, more sucinctly:
"Not killing Hitler is exactly what you don't build a time machine not to do." - Jennifer, 12 Monkeys.