Indeed.
Primarily, from a Spurs point of view, CE will know he's 'stuck' here if he doesn't perform.
Would still somewhat suprise me if CE did sign the rumoured deal though as it puts US firmly back in the drivers seat again, whereas he had/has us by the balls currently.
If at all genuinely interested, I certainly think RM would have been rolling the dice on getting him for nothing next summer.
Let's face it as fickle as they are, RM (club and fans alike) will be all over him if he has a good season and their current revamp isn't going according to plans.
I'd guess that Eriksen has probably been told that Madrid are not desperate to sign him atm.
I'd also guess that DL will recognise that Eriksen would like another chance of his dream to go to Madrid and at the same time had enjoyed his time at Spurs, so might well offer a long contract that gives Eriksen a long term future at Spurs but with an option that if Madrid offer say £100m in June next year that Spurs will accept, but otherwise he stays for another 4 or 5 years
And on that basis it's a win win for both Eriksen and Spurs.