Whether you take the money and run depends on whether you think Nexus can make you more than $150,000 if you stay. I'd say, especially with the coming influx of NXL teams, that you should take the money, as otherwise you're probably just going to lose the spot next year and get $0.
Unless playing NPPL for one more year is worth $150,000 to you, or you're willing to majorly change your roster, which might make it more interesting to stick around.
However, who says NPPL is going to honor the 18 spot system? I can't imagine the PSP/NXL guys are going to merge with NPPL without getting some spots in the deal. Are they going to just add more spots, or are they going to boot some teams?