An ability that triggers when another ability resolves, such as Tom Bombadil's triggered ability, triggers when all of its instructions (as modified by applicable replacement effects) have been followed and it has been removed from the stack. For example, if Tom Bombadil is returned to the battlefield by the final chapter ability of Elspeth Conquers Death, it will be on the battlefield in time to see that final chapter ability finish resolving and get removed from the stack, and thus Tom Bombadil's last ability will trigger.