A client asked us to have access to the source code of our app they are using.

The thing is that this app is made for a vertical market. So there is no way that they'll get the source code right away.

What would be the best thing to do for everyone is to make the source code available in case something happens to the company and that they end-up with nothing.

That's the situation they want to avoid.

Should they have to pay a premium because right now they pay for a fair amount considering that the app is also sold to other businesses. If they get the source code then it's another thing because then the amount they paid (license) would'nt seem to be enough to get all the source code.

Now what do you think would be the best deal for everyone?

What should be considered in that kind of deal?

What kind of clauses?