The priest in choosing to break his vow commits adultery against the Bride of Christ, the Church and the remedy would not be for said priest to continue in mortal sin. There are no easy answers because this is such a huge rupture of faith/truth/love.
Must we lose the services of the priest who resigns and marries honestly?
Firstly, The Church has a permanent diaconate that would suit many men that want to serve the Church as married men.
While there are certain things that can happen in life that are out of our honest control there is nothing honest in this situation. There is a big lie regarding the vow. The same is true of many a divorce.
Quoting pious poetry about "a priest committing adultery against the Bride of Christ" is an insult to the heterosexual men who are priests. That line would fit better in a soap opera or on "The View".