I think it would be foolish to assume that neither is a long term answer because of injuries, one of which isn't even out for the rest of this season.
I agree, don't sign either to a contract this offseason, but they already said they plan to discuss an extension w/ Mooney. And again, it would be foolish to completely dismiss the idea of signing Claypool after you gave up, what is right now, the 33rd pick for him. So, clearly both are at least in the long-term plans, if only in pencil.
And again, Lazard/Slayton/Meyers are all not as good as Claypool or Mooney (based on everyone's most productive seasons), so I don't see the point in paying them good money to potential hinder the ability to sign Claypool or Mooney if they do work out.
The Bears are basically between a rock and a hard place. It's Claypool and Mooney or bust at this point. They made the trade partly because of the lack of talent in this FA class. They can't afford to give up another early pick for a true #1 WR. They aren't in position to draft a #1 WR, if there even is one in this draft. And they have to at least keep the option of paying Claypool and Mooney long-term open, signing a FA to a multi-year deal at least partially closes that option.