It's not common, but it's not unusual for solicitors to take the fees and not get around to finishing the paperwork.
The main issue here is that you apparently do not have title to your property. That is the key issue which you need to address as quickly as possible and fix. If you ever try to sell the property, you will have to fix this and it might take some time, thus delaying a sale.
If the solicitor has ceased practice, some provision must have been made for his work to be completed.
You should contact your retired solicitor to find out what the story is. If he does not respond, ask the Law Society to contact him.
Of course, if the lender is prepared to fix the title problem at their expense, that is fine. In any event, I think you will probably need your own solicitor to make sure that it is done properly this time.
If you are in deep arrears and deep negative equity, you might be able to use the confusion to get a deal on the sale of the house and the write off of the shortfall.
Brendan