I think you have to focus on the one issue, his swearing and subsequent suspension. Everything else that you've mentioned is irrelevant to this - sick days, holidays etc etc (it may be important but as a separate issue and I wouldn't even bring it all up at the moment).
Swearing at work, especially the use of the F word, would, in most cases, be regarded very seriously, probably gross misconduct. Given that it was done in front of a member of the public (the time of day and whether the person was apparently bothered or not is largely irrelevant) makes it worse.
I would have thought, in the circumstances, they have done the right thing by suspending him while it's investigated.
In different circumstances, for example if he had been bitten by an animal, and had sworn due to that then I think it would be regarded slightly differently, but to swear at another member of staff (a manager?) in front of a member of the public would be considered completely out of order.
If these are the facts of the case, leaving aside all the other issues, then I would suspect that, as a minimum, he would be given a warning as to his future behaviour. It could, however, result in dismissal as many organisations would regard it as gross misconduct.