When Barry Sheene found and developed a young rider by the name of Chris Vermeulen some years ago it was the wish of Barry that he (Chris) ride in Motogp and that he use Barry's race number “7”.
At the time someone else had the number and Chris used No:71. By the time “7” came around Barry had succumbed to cancer, and Chris having secured the number was fast tracked out of Motogp, after winning Suzuki's only ever 800 race in what could have been a submariners event at Le Mans in torrential rain.
Give Loris some ownership over the number but don't retire it, if he mentors a younger rider or wishes to see a particular rider race with that number (a relative, some from his hometown or whatever) allow Loris to grant the permission and also bit a time frame like 10 years on this (only to be extended if Loris is still with the sport and is bringing junior riders along with the sport).
That way the number will still be connected with Loris and still represent the effort he is putting into mentoring the future champions.
I still think a riders number should only be retired when he dies during a racing incident.