Cloud and Tifa are analagous to Guts and Casca
I mean this in the sense that both are so fundamentally inseparable that these stories would be impossible without them being in love. To explain what i mean, casca is the only person that wards off the darkest part of his personality that manifest in the beast of darkness, if we were to hypothetically say that she died during the eclipse than there would be absolutely nothing stopping guts from completely succumbing to his jungian shadow. While yes, he did go after revenge post eclipse he eventually was reminded of how selfish he is by godo for not being there for her and rickert in the most difficult of times, he changed his ways, from that point onward he decided to do anything that would even resemble a chance of restoring her mind. On the other hand, Tifa is inseparable from cloud (and quite obviously in a romantic manner, this shouldn't be up to discussion but alas) because she is the only remaining part of his life before his mind was wiped. ONLY Tifa can know who the real Cloud is, that is why she is the only one capable of repairing his mind in the lifestream, because the entire reason that Cloud was on the journey to become a SOLDIER is precisely to impress Tifa and because of the promise he made to her, quite literally, Tifa is what makes him whole in the end brings out his truest self, we see this not only with her saving him in the already mentioned lifestream sequence but during the entirety of both the OG games and the remakes too, you can tell that he feels more comfortable with being himself around her compared to everyone else (we see this in the high affection hug sequence in the first part of the remake, where his true self is there just for a moment when he comforts her). So while yes, Aerith dying did install crippling depression and A LOT of guilt into cloud, Tifa dying in her stead hypothetically would absolutely break him, because, in a way, Tifa is A PART of Cloud.
Anyway, thank you for listening to my TED talk i just had this on my mind