Even if you are correct about your emotional state affecting your ability to compete fairly, you would have a hard time proving your employer hadn't done all possible to re-deploy you.
In relation to the people on maternity leave...they come under different rules in these circumstances. They have an advantage (to protect against discriminating against women when pregnant) in that when they go on maternity leave and their jobs are filled in the interim, or if management changes occur whilst they are away, they must be able to return to a post that is equal in status and salary to the one they left temporarily, or they certainly COULD sue for constructive or dismissal.
Talk to your union or consult an employment lawyer to obtain an impartial view on the deal being offered and the circumstances. If nothing else it will reassure you that you're getting the best offer that could be won.
It won't alter your perception of how you're being treated after years of faithful service (a personal and emotional reaction) but will help you understand the cold business approach.
Been through it, and found there's life after the pain.
Good luck