While the CDMA backend is basically dying, the radio side of it isn't. EV-DO Rev B is fairly recent, and a lot of the CDMA designs were incorporated into 3G GSM (hence "W-CDMA"). CDMA phones are still crazy popular, and it's going to be years before CDMA is completely shutdown.
The biggest challenge is LTE expects a GSM backend, but eHRPD fixes that, and Verizon, MetroPCS, and yes, even Sprint, have deployed it successfully. Sprint already has a LTE network, after all, and their SprintLink backbone to help backhaul it.
The biggest question is WHY Clearwire. Sure, they own a ton of spectrum that Sprint donated to them. But with Sprint being the majority shareholder, I'm not sure what DISH thinks they'll be able to accomplish.