I spent 3-years in France with that blue recipisse. It's equivalent to the CoA provided by the Home Office when you lodge an application.
It's common for the French authorities to play a despicable game with applicants: when you are entitled to something and they don't want to give it to you, they just delay delay... They hope you will get tired and leave, or the law changes for the worse... etc. In my case, they used to tell me "oh sorry, but your documents are now too old, you need to submit fresh ones again."
As for your wife, I don't recommend she lets her document expires. It would be a very bad idea.
There is a visa called Return Visa ("Visa Retour" or "Visa de Retour") but this one is only for people who actually have a valid residence card or a Recipisse that expired or was lost while they were abroad. It's delivered in "exceptional circumstances" by French Consulates after consulting and seeking the authorisation of the French Prefecture where the applicant lives.
Here is a page in French (French Consulate in Ouagadougou, Africa but the process is the same everywhere).
https://bf.ambafrance.org/Le-visa-de-re ... un-visa-de
They really insist on the "exceptional" and "discretionary" nature of that visa. They want a "detailed letter" explaining how come you need such a visa. If she tells them she let her Recipisse expire on purpose because she prioritised some professional commitments abroad over returning to France, they might not like it.
It's a risk to take really. It's up to you guys to see if you want to risk it or not.