You can still setup a forwarding address and change the reply-to address, so users can use regular Gmail for free. It just means that your company will not have control over the account.

Unfortunately, I don't think threatening to leave when you're not paying anything is really a threat at all. $50/year per year is still pretty reasonable for the services provided.

The other option is that Google retires this feature completely, as they've done with other services people might have been willing to pay for, and that seems worse as you have no choice.