I have a 2014 ex800 zforce with only 850 miles.  Brought to dealer as it wasn't running right.  Within an hour they diagnosed total engine failure.  $5000.      Does anyone know of options / rebuilds / aftermarket? 

Your option is to take it to another small engine shop where they will not try to screw you over.
You stated "not running right" which indicates that it has not completely self destructed and can probably be repaired.

Can you elaborate on what exactly the problem is and why the dealer said the engine is toast? 

[2015 Z Force 800 53/Trail EPS]

If you can do the R&R yourself, talk to nFlow about remanufacturing it. I trust them and they will do CFM engines. There are also other places that rebuild that may be a good option.  Or you can buy a complete engine from Alpha-Sports for 4042.50 plus shipping.

Can you elaborate on what exactly the problem is and why the dealer said the engine is toast?

Lets start with this.