After One More Day, some fans suggested possible compromises for Marvel as ways the status quo could have been changed without a retcon. One suggestion to get rid of the marriage while preserving the commitment to change was that Mary Jane could die in childbirth. This would leave a single Peter Parker having to take care of a newborn. His life certainly wouldn’t be easier, and the status quo wouldn’t be stable. It would emphasize Peter’s youth as he can be portrayed as a young man in an extreme situation.
Among other problems, this requires the death of a good and popular character, and it is unlikely the writers could keep the child’s age fixed, so it has some of the problems with making the character a married father. As it could also lead to readers blaming the kid for the loss of a beloved character, it’s worth tweaking any such story so that Mary Jane dies an year or two after the kid’s birth (or after Baby May is found) of non Spider‑Man related causes, so the infant can be seen as a miracle as opposed to the cause of death. But I still don’t think it’s a constructive development for the series.
Another compromise some readers have suggested is that Peter and Mary Jane adopt a baby. This approach has the same problems as giving them a biological child (without the stories you could get only get from a pregnancy), especially with what it means for everyone else in the Marvel Universe when the child grows older. Unless the kid turns out to be a Skrull. Which would probably be “Doctor Octopus marries Aunt May” bad.
There’s an alternative way of telling that story. Marvel could kill off Mary Jane’s sister in a car accident or in the crossfire of one of Spider‑Man’s battles with a supervillain the next time she visits the Parkers. Peter and Mary Jane might take in her kids, though that also has its problems. Having Peter Parker become one of the primary caregivers for two kids will make him seem significantly older. The new kids would likely overwhelm Peter Parker’s private life, though it is a change that could be reversed once their father finds out about his ex‑wife’s death, and sues for custody. Although I don’t know if that’s an effective subplot for this particular series.
One problem with compromise solutions is that there is nothing Marvel could do with the book that would make everyone happy. Any change to the marriage would have upset some fans so Marvel shouldn’t take some fans getting upset into account when determining what’s best for the entire franchise. Although it’s worth noting that Peter and Mary Jane having a child in the regular Marvel Universe is a change to the status quo which would alienate many Spider‑Man readers (those too young to have families, the pathetic older readers who will never have families, the not so pathetic readers who have chosen not to have kids, the readers with bawling babies or teenage delinquents who want escapism from their own kids, etc) even before the stories start getting dull and repetitive, which I expect would happen long before the twentieth year of Peter and MJ as the parents of children too young to be superheroes.
A simpler retcon than One More Day would have been the revelation that the the Mary Jane Watson Peter Parker married was a Skrull, tying the Spider-Man books to Secret Invasion, an event book Marvel was seeding at that time. It’s a plot that has been done before (see Johnny Storm and Alicia Masters or the 90s Fox Spider-Man cartoon.) In defense of the suggestion, it is worth remembering that while the Alicia Master is a Skrull plot isn’t exactly remembered as a high point of the Fantastic Four’s history, it did accomplish its job of making Johnny Storm single again, while reestablishing Alicia Masters a potential romantic interest for the Thing.
The Mary Jane you knew and loved was an evil impostor plot would have created a bad subtext for every story about their marriage, making the relationship completely insincere. One More Day didn’t retroactively change the motivations of the characters, or anything about their identity and motivations in earlier tales. Even if there’s brainwashing involved so the Skrull agent thinks she’s Mary Jane, this would result in all sorts of complications of the convoluted kind, rather than the good dramatic kind. It would be referenced often, as others in the Marvel Universe would be expected to bring up the subject.
If the world doesn’t find out about Mary Jane being a Skrull, Peter Parker will be considered a divorced man. If Peter’s problem is made public, it’s something that would put him under public scrutiny. Neither solution is preferable to a magic retcon. Although there were some non-retcon alternatives.