What to do that wise would not disappear again? My person, just seeing that you are certain gifted to be, possible not so aware, gifted to have another Noble one around here thought it would be good to be asked an importand question:

What needs to be done, what should a community take care of, in the case someone more skilled in liberating means would approach?

How does one "bind" such a blessed gift?

[Note: this is not given for stackes, exchange and trades in the world, but to get bind toward liberation. Should be deleted if place does not have interest in releasing it's visitors.]
There is a good book about community building; Community Building on the Web : Secret Strategies for Successful Online Communities – by Amy Jo Kim.

The most knowledgeable people are those who are able to answer almost any questions. They are extremely valuable but are also quite likely to retire from a community in part because they don't need the community to learn and their lack of peers is proportional to their expertise. 

If one is looking to keep the knowledgeable people around one should protect them. They do need to be protected from harassment and it is the job of the moderators. The moderators have to work with them and this can be difficult.

Other than that they can also just lose interest in teaching or become otherwise disinterested.

Related Sutta stories;

There is a story about monks quarreling and the Tathagata leaving the community because the monks did not settle their quarrel.

There is another story about The Buddha not teaching in an "impure" assembly which results in a monk being removed by force from the assembly.

Another is when Ven. Sariputta stops teaching because a monk harasses him by openly disagreeing in front of other monks and nobody defends Ven. Sariputta. Later Buddha admonishes the monk for harassing Ven. Sariputta and admonishes the community of monks for not defending the Elder.