Working on a real ending for Malec (because I cant satisfy with their ending in CoHF), here are what I come up so far:

First Magnus has to die. For whatever reason you can think of, but prefered a heroic one, for example saving Alec from a demon attack. They (Alec & friends) then summon a demon (it can be Magnus’ father to add more drama for the situation) to try to save Magnus from the death. (According to Cassie, powerful demons can do that, because Simon is technically dead before he becomes a vampire, now he is still alive. And Jace was dead once too)

Well, you know, because ‘All magic comes with a price’ so they have to pay something. and the demon want Alec’s life – a life for a life. Alec of course is willing to pay it, but others don’t let him it. So they come up with a solution, all of them will give up some years of their life.

For example, Alec’s fate is to live until he is 50, so he has around 30 years left, so the demon wants to take 30 years of Alec’s life. But instead everyone of them give up 6 years (6×5=30) – i only count Clary, Jace, Simon, Izzy & Alec here, but you can add more characters if you want, the more characters the less years they have to give up. 

But the demon thinks it’s too easy for them, so he want to add more condition: All the years Alec has left (30-6=24), he will have to give half to Magnus, so both him & Magnus can only live for 12 years more.

And last condition (because i’m a cruel person) is a classic one, when Magnus wakes up he will forget everything that ever happened in the TMI series, from the day he met Jocelyn Fairchild & baby Clary. He is still a warlock though (but he will have no idea that he can only live 12 years more). Don’t worry eventually he will remember just like Simon, but it will take a while, about 1 or 2 years.

With these, finally Magnus can get rid of immortality, they can be together but only for 10 years (honestly it’s quite romantic when you think about it, they can die together AT THE EXACT SAME TIME how cool is that huh. Imagine both of them curl up together on a bed, whisper I love you to each other before both pass away, they can literally die in each others’ arms)

Yes, that’s my final solution for Malec. What do you think? Is it bittersweet enough or should i add more? Maybe 10 years is too long, should i make it 5? (And at moment like this i wonder if i’m a sadist). Of course there are a lot of plot holes (for example, demon always want something that benefit them but all theses condition doesn’t benefit anyone at all) because i just think of it an hour ago, i’m still trying to solve them so the story can be more realistic

P/S: Feel free to use this idea for fanfiction, because i cant write & i do want someone to write this. Just dont forget to send me the link when you finish :3