tbh there are still plenty of players who maintain their test careers alongside franchise riches despite the relative lack of rewards. Many of the New Zealanders do this (Williamson, Boult, Southee, Jamieson, and before them the likes of Taylor and McCullum) - they earn way more in the IPL than they make in the rest of the year, but that doesn't diminish their commitment to NZ, and the NZ board are pragmatic in allowing players to fly in for games at very short notice. And there are examples of players skipping an IPL season to concentrate on red ball skills - Kyle Jamieson's just done it.
Some way needs to be found to face up to reality and create a proper window for the IPL in return for windows for test series, at least those that are part of the ITC. What devalues test cricket most is having series like the current SA-Ban series in which all the SA IPL stars are absent. Indian players are fortunate in that regard. If you look at someone like Virat Kohli, he basically plays IPL and for India and virtually nothing else. Most of India's test stars follow that pattern.