I just found out my friend who is 75 has Parkinson's. What do I need to expect and how long will he be around?

Kruss, something you might consider is learning about Dance for Parkinsons, and determining if there's a chapter near you and your friend. 

It's a movement started by a professional ballet dancer who with other dancers adapts movements for those with Parkinsons.   There's no leaping, or en pointe dancing but rather slow, graceful movement, standing up or sitting down. 

It's more like a graceful Tai Chi workout.    Apparently it helps maintain movement as the disease progresses.  
 
https://danceforparkinsons.org/

Note that some dancers do so while sitting down.

I read something that most patients don't die from Parkinson's but their lives are just diminished due to the disease.

My mom is 94 with Parkinson’s. My uncle was 96 at the time of his death. He also had Parkinson’s disease.

He can be around for quite a long time, actually. Here is an excellent article from the Mayo Clinic explaining the disease:

https://www.mayoclinic.org/diseases-conditions/parkinsons-disease/symptoms-causes/syc-20376055

And here is a link explaining the 5 stages of Parkinsons:
https://parkinsonsdisease.net/basics/stages/

You are a very thoughtful friend!