That is actually the way it is done in a lot of areas. They use it as what is called "wood buck". It is attached using masonry anchors to the concrete an then the window is installed normally.

Decent quality sliding - or folding sliding doors - will do the job and last more than 15 years. Of course you have to fit them properly for a good seal so choose an experienced fitter, a specialist fitter or buy a door that can be fitted by the manufacturer. As with anything, you get what you pay for. Untreated softwoods are likley to warp over time so treated woods, hardwoods or metal doors will perform well over a longer period.

I replaced a very large casement window in my family room( 108" x 72") 2 years ago for the same reason you want to change yours out. I had this done while we were replacing all of the doors and windows in the house. The door, which is a slider, not a french door( due to space constraints) has divided lights and is 108"x 80". It was 1500.00 installed. YMMV. Check with several door distributors as well as the big boxes for estimates. It believe it will depend on how much framing is required and which door style you choose.

You are welcome. I'd use WoW if they were here (same area) for my own house LOL. Anyway, the sliding door is under-serviced no doubt. And it's been replaced a few times as well in the last 20 years. Basically, there is something going on where a lot of debris and water get into the track. I think the exposure directly to the outside and a lot of yard debris (leaves, dirt from the ditch that blows up in windy weather, etc). And that starts the downward decline. Perhaps the last install was bad. But we really want to do away with a slider completely this time and simply avoid having to keep cleaning the track and servicing it. Even with a new sliding door, the shoulder surgeries have left their arms weak and I think it's best to avoid that type of door going forward