I had to run hypo in my 90 gallon (110 total volume) FOWLR at one point.
Personally, I would remove 50% of the live rock (stuff with the most visible life on it) and leave 50% in. The thing to remember is that protein skimmers basically don't function at a salinity of 1.009 so keeping some of the live rock in the tank is (in my opinion) pretty essential to maintaining semi-decent filtration during hyposalinity.
Any macro-organisms like spunges, feather dusters, polychaete worms, etc on the rock you leave in the tank will die off, but the beneficial bacteria on the rock will remain. As long as you make a point to monitor ammonia very closely during the first week or so (test at the very least once each morning and once each evening) and do water changes if necessary.
The final thing to remember is run hypo for the full 6 weeks no matter what (and make sure to use a refractometer to test salinity instead of a hydrometer). This will give any dormant cysts on the live rock you removed time to die. I made a terrible mistake running hypo on my FOWLR tank and stopped right at the 4th week. A few days after bringing the tank back up to natural seawater levels, the ich returned. It was seriously such a terrible feeling of defeat that I almost gave up the hobby. I started hypo over again and ran for a full 6 weeks and all has been great ever since.
Once the hypo was over, I put the removed rock, snails and hermits back in the tank and within the week I began to see life popping up all over the tank again.
Hope this helps... I know how stressful the situation you're in can be.
-Julian