What will happen if wildfires spread across the world?

They won't.  Most places use rational forest management techniques to prevent large fires like this.  California in their eco-insanity just lets them grow -- No brush removal, no fire breaks, no controlled burns or logging to reduce density.  A relative out in California has had a dead tree on their property for almost 10 years, and the government of CA won't let them cut it down.  Lot of just plain stupid people out there. 

Once they reach the ocean they would burn out by itself.

If you start to see wildfires in the North Pole area or Antarctica then I would be worried.  In general fires don't spread well across the Pacific Ocean.  Water doesn't burn well.  But in country after country we are having more wildfires covering more area than have been recorded in history.

spreads , see the seas on fire , sounds like a movie to me .

Indeed they will not.   For instance:  Much of Britain is simply not wildfire terrain.   A  fire of about10 square miles did break out on moorland last year but did not threaten to run for dozens or hundreds of miles as wildfires run in parts of Australia and the USA.

Much of Europe likewise is not really wildfire terrain.

There are some areas that won't burn.

they couldn't make it past the mountains AND then the Arizona deserts to the east ...........