Both places you mentioned are still open although La Fortuna is nowhere near as busy as it used to be.
Best paella for me is at Raymonds 1 which is on the right on the main street in town going down to the beach (just past the Carolina supermarket)
So many places to eat that its hard to make a recommendation, can't remember really when I last had a bad meal in Tenerife.
You will find a lot of changes if you havent visited for a few years - if you like walking you can walk along the promenade all the way from Los Cris into Las Americas. If you do the walk then do try the Gran Paella Valencia for the biggest steak you will ever see - its just before Puerto Colon, go past the Jardin Tropical hotel (beachside) then you will come to a mini roundabout, the restaurant is on the corner there, recognisable by the crowds.
If that is too full then go next door but one (ignoring the Aberdeen steakhouse between them) into the Vista Del Mar restaurant, but go upstairs for the nice view - same menu etc as Gran Paella as apparently family owned.
Have a good time, sure you will.

thanks v-m i shall take a note cos my memory is terrible, we used to go to fortuna at least 3 or 4 times on every visit to los chris,and the same with la cava in my oppinion, the best two eateries in tenerife, but its been about 8 or 9 yrs since my last visit,been to other end for a/i due to kids but now they are growing up so can go back to s/c