I'm of the same mind. Two years is a long time in football and he earns a relatively modest £65k a week, so it would be costing the club peanuts to keep a genuine game-changer in the squad mix.
The only issue comes if that results in a lack of professionalism from him. We don't need the money, though. We shouldn't care what other people think if we allow a 25-26-year-old coming into his peak to walk away for nothing.
Lewandowski did so.
We can still afford to go out and buy his long-term replacement. Sane and his advisers just need to know that we wouldn't be bluffing and any lack of professionalism won't force an exit.
In that respect, it would be up to Sane's side to convince Bayern to pony up the suitable price now.
Lack of professionalism/acting out would be very unwise if he wants to go to the Euro's in 2020. 65k/week is only 3m a year, an almost insignificant number for a club with £600m revenue.
He could easily be made to sit on the naughty step for 12 months and watch another international tournament pass him by if he and his agents try to force something.