He was still filming NCIS, so he probably wasn't that sick until very recently?
Peter David says Miguel O'Hara/Spidey 2099 was named after Ferrer:
Miguel was a friend. I met him through Bill Mumy and although I haven’t seen him in years, he was never far from my thoughts. I named Miguel O’Hara after him and still remember when my editor challenged me on the fact that his nickname was “Miggy,” declaring that it was not a nickname anyone used for Miguel. Which was hilarious since that was what we all called Miguel.