The situation is not an all or nothing as you have outlined. Maybe we get regime change, maybe we don't. Another outcome which we have basically already achieved is a substantial depletion of their nuclear program, navy and leadership chain which will indeed take years to rebuild. It's hard to fight back against the enemy when your new leader has to constantly go into hiding and carry the paranoia that they'll be blown away upon acceptance of their new leadership position. The world is a power vacuum, if we sit back and allow them to operate with no pressure, they will pursue nuclear weapons and continue to fund terrorism around the world as they've done for the last 50 years.