I'm actually not too "up" on the MPL, so stand to be corrected, but I believe a key component of MPL is that it requires an airline to "sponsor" (for that, actually read "have pre-offered employment") a student prior to them starting the course.
Therefore if we follow this logic and ask the question, does it mean the death knell for fATPL, then the answer would probably be "no" as it would require all airlines to accurately forecast the number of low hour pilots they need, would necessistate all who started finishing and would remove flexibility. If I'm right here, there will always be a need for airlines to pick up more pilots as and when required...and these additions would have to come from the fATPL route.
Therefore, I'd suggest that the more likely outcome is that airline "tagged" schemes such as FlyBE, Netjets, Citiflyer etc may become based around the MPL - hugely dependant on the individual employers and their view of MPL - but there will still be a huge [majority of low hours?] market for those who study the currently more established route of fATPL.
Like I say, I don't know too much about it, so stand to be corrected on this, but my tuppenceworth.