Is the life expectancy for people with dilated cardiomyopathy 5 years after their symptoms begin?

Depends: Depends on how severe it is and how well it responds to medicines. Some may recover, some may be stabilized with medicines, some may require heart transplant or die.

Varies: There are different severities of this diagnosis. You need to disuss this with your physician because it is impossible to answer without more detail. Even then predicting with something like this is very very imprecise. But it is not a good diagnosis. The next step is heart transplant.