I have an idea! Why doesn Giles try to figure out a way to make Angel back into a normal person again?
One theory is that if Angel were not a vampire, he would turn into a 243-year-old man – and die. The prevailing theory is that the demon is what keeps him alive. A spell to exorcise the demon may also be difficult to execute. The demon has also proven useful in fighting off other demons (see The Dark Age). On the other hand, on a recent episode of Angel, Angel was made human, with disasterous results.