You may have heard it’s now a TV series: The Mist (TV series) - Wikipedia
Here is one.
“28 Days Later” ends with the good guys (and gals) surviving. But by no means has the zombie apocalypse ended. Hence “28 Weeks Later” when the humans are “winning” and attempting to re-populate. But there is still a zombie (and virus) threat present.
The end of the “World War Z” movie has the humans able to combat and destroy the zombies, but they don’t really indicate that they’ve found a “cure” for the virus which converts humans to zombies. They are still trying to just destroy the zombies now that they’ve figured out the means to not be overrun/overwhelmed.
As I recall, the protagonists were happy to see a European jet, indicating the virus had not spread beyond the U.K. That’s about as upbeat an ending as could be expected.
Ditto.
Warm Bodies I guess beats the above two because there is a cure for zombitis:
It’s love.
Per the OP: “What horror movies in the past 35 years had good defeat evil, without hinting that maybe the monster or killer is still alive or will return?”
“28 Days Later” and “World War Z” may have ended “up beat”. But not quite what the OP was asking for.
There is an alternative ending that wasn’t happy though.
1408 had a happy ending, I guess. Case 39. Friday the 13th part VIII. 28 days later. I guess it depends on how you define happy.