It seems to me like the Paris attacks were, from the standpoint of someone who is not an apocalypse cultist, the worst decision strategically they could conceivably make. Like, starting a land war in Asian part of Russia in winter to attack Pearl Harbor-tier bad.
How so? ISIS spent 10K USD in equipment, plus let's guess something along the lines of 1M USD in human assets and in result inflicted direct damages in the hundreds of millions. if the UK and France start escalating their bombing in Syria and Iraq and it appears they will, it translates to additional hundreds of millions (Conservative estimate). the tightening of the security in France and Belgium cost additional hundreds of millions in spending and lost revenues (Conservative estimate) since they are basically paying for people to just stand in street corners and scare innocent people off.
On the other hand, it is entirely possible that the Paris terror attacks generated significant revenues from donations to ISIS. it is also quite possible and reasonable that it also generated a fresh stream of recruits.
They have achieved their goals since they had made their enemies lose a couple of billions, disrupted the population and terrorized it to such extremes, that i dare any European cartoonist to portrait Muhammad shagging a pig signed under his own real name. ain't gonna happen and not out of respect. as for the west invading them and meet them at the battlefields, well, that's actually one of ISIS goals.
As for the fantasy of France, the UK or the US achieving their goals and demolishing ISIS through air strikes, then they will have to also bomb in Saudi Arabia, Qatar, Libya, Algeria, Turkey, Indonesia, Pakistan, Yemen, Tunisia, Israel, the Palestinians, Jordan, Lebanon, Egypt, France, Belgium, the UK, Spain, Bosnia, India, Russia and a bunch of other countries in order to demolish ISIS and that's simply not going to happen. if, for some obscure reason, the french suddenly become competent and do manage to eliminate the entire ISIS leadership in both Syria and Iraq, very soon new leaders will emerge and history taught us that eliminating a leader does not necessarily ends an organization. you can call them ISIS, you can call them Daesh, you can call them Al Qaeda in Iraq, you can call them Al Qaeda, you can call them Mujahideen, you can call them Jihadists and you can call them Islamists, it doesn't matter, Crush one, the other will rise.
You are also forgetting one little thing. the US had its "Pearl Harbor", it was called 9/11. they went to war. they didn't win this time.