Discriminatory, unlikely. Crappy, yes.
First things first maybe sort out your PHI so you’re not left out in the cold when the time comes. They might allow you to pay off the remainder of your premium in a lump sum now and put arrangements in place for continuity when you are off e.g. they could take an amount for the premium and pay it for you at renewal time.
From what you said they seem to be meeting their obligations legally. I assume it’s a small company you work for? It’s a tricky area for small business and I’m sure they would love to do more but it’s a significant outlay particularly given current circumstances.
However, if it’s not the above and it’s a healthy business or it’s a business that touts any sort of social credentials/“gender balance” or has published a policy/advertised using the words “diversity” or “inclusion” in it then it’s free fire in my opinion because it’s disgraceful.
In reality you don’t want to go down the discrimination route, it’ll be unpleasant for everyone. You would have to establish if they have a different policy for other types of unpaid leave? Do they pay paternity leave at full pay for example? Even then you’d have to go through a rigmarole that you don’t want.
But on the plus side you you have no obligation to your employer once you’re off the payroll. Do yourself a favour and look for something more suitable for your circumstances.