Mac's 42 day suspension following his behaviour in Stockholm, was reduced to 21 days (a condition was that he didn't play in any exhibitions during those 21 days), allowing him to play in both in the Australian Open and Davis Cup final.
Many of Mac's suspensions, including that one most likely, were by choice. When he wanted a break, such as near the back end of 1984 when he was getting tired, he'd behave badly on purpose to exceed the fine limit and trigger the resulting suspension. That saved him the hassle of withdrawing from tournaments he couldn't be bothered to play in. So I think it's pretty likely that had the grand slam been on the line after the US Open / ahead of the Australian Open, he wouldn't have got suspended in-between in the first place.
If he’d won the first 3 majors of the year, it's difficult to say what his scheduling should have been to maximise his chances of winning the Australian Open 2-3 months later, striking a balance between sufficient rest and sufficient match action to keep sharp. There were no grass court tune-ups for the AO, with Sydney held the week after (the same week as the Davis Cup final). There were indoor tournaments in Australia in Sydney (a highly regarded tournament) and Melbourne in October, but then then 5 a week gap until the AO started, and so he couldn't have spent all that time Down Under. I've said this many times, but before the ATP standardisation in 1990, the set-up of tennis was significantly less conducive to allowing players to prepare for and peak at the grand slams.