I can buy 50 RV MPs. That does not mean the support for URP or Ruto is gone down.
Let's look at Ababu: He cannot win his seat without Raila. 2/3 of the constituents are ethnic Luos with a fanatical following for Raila. The same to Otichillo whose Emuhaya spills in to old Nyanza. Raila is simply put too popular in those areas and may not need these MPs.
Before you say much see who got most votes in Vihiga between Raila and Mudavadi.
However you are right. The MPs need money. But I disagree with you insinuation that MPs voted for opposition should abandon their party and run after cash from government. Then you might as well just support Mono-Party politics.
Raila also bought ODM mps using gov largesse and patronage. Those MPs are waking up to reality of 10-20yrs in opposition benches and it doesn't look great. Outside Luo Nyanza ODM strenght has weaken. Those Mps will win or lose depending on local issues at play.