I am so sorry about Diesel. I can definitely understand your fears. I think it is important to let go of your irrational fears, but you'll have to determine what is rational and what isn't.
I think recall is important even if you did absolutely never plan to have your dog off leash. You never know if you'll accidentally drop the leash while fumbling with other things, the dog will think it is coming outside with you and dart out without a leash on, or any of a million other circumstances. Heck, I've had collars and leashes that seemed to be in good repair break on me! So training a solid recall is important for every dog.
I also think we have to be realistic and realize that they're dogs, and sometimes even highly trained and reliable dogs aren't going to be perfect. My dogs have as close to a perfect recall as you can get, but I still don't let them off leash in busy traffic areas because all it would take is a second of me not paying attention (so not actually calling them back), or a one-time lapse in the dog's focus or response, and disaster could happen, as you unfortunately know.
So, if I were you, whether I would let my dog off leash in the yard would probably depend a great deal on the actual circumstances. If you're close to a busy road or one with a high speed limit and/or low visibility, then I would say it isn't worth the risk. Your dog will be out in that yard a lot
in the course of her life, and the chances of her running off at some point are pretty high. Now, the chances of her running off and getting hit by a car are actually probably pretty low unless the road is extremely busy, but it's not a risk I would take and it doesn't sound like one you're comfortable with either.
So, I would probably either fence all or part of the yard (you can do it cheaply and easily with livestock fencing), or keep her on a leash. I'm not a fan of tie-outs either, but I think that as long as you're just using them to let the dog relieve itself and not making the dog sit out in the yard forever, they're not a big deal. I prefer to take mine out on a leash when I've had to do that, because to me tie-outs are a bigger hassle than having to walk around the yard for 5-10 minutes. It's good exercise if you have to do it several times throughout the day.
Then for safer areas where you're not right by a road, like when you're camping or at the beach? Train your dog, test the behavior, then trust her.