Could Betelgeuse already blown up

It's possible, yes. Betelgeuse is a red giant star that is going through the last stages of life, as viewed from earth. The light from the star takes several hundred years to reach us though, so it's possible that the star has already come to the end of it's life in that time. When it comes to the end of it's life it will explode in a supernova explosion. We should be able to see this from earth, the explosion would be so bright that we could see it during the day.