Maybe it could ally with some people and give them tech/power in exchange for carrying out its bidding.

Some AI's already do this today. The outsource work they can't do to Amazon's mechanical turk where humans get payed money to do tasks for the AI.

Other humans take on job on rentacoder where they never see the human that's hiring them.

Even with what you describe, humans wouldn't become extinct, barring other outcomes like really bad nuclear war or whatever.

Human's wouldn't get extinct in a short time frame but if the AGI has decades of time than it can increase it's own power over time and decrease it's dependence on humans. Sooner or later the humans wouldn't be useful for the AGI anymore and then go extinct.