What is your planned asset allocation post-FIRE? Are you planning to have some portion in bonds or cash? Or are you planning on just having everything invested in the market and selling at periodic intervals?
I think immediate pre-FIRE planning is different than the "getting to FIRE" planning, because now you have to worry about market drops and where to withdraw from and all that. IOW, your priorities shift from solely growth to some combination of growth and risk mitigation (i.e., avoiding massive losses that would send you back to work).
So for me, for example, I plan to have a couple of years' expenses in CDs or bonds, to give me time to ride out market drops. But I don't intend to start buying them until a couple of years before I call it quits, because I don't want that drag on performance while I'm in the growth-only priority phase. So if that's your plan, then I think you are close enough to FIRE to just hang onto that cash -- you're now at the phase where you should be starting to compile those "safe" assets, so it's fair to use this windfall to do so. OTOH, if your plan is to stay invested at a particular asset allocation, then you should deploy that cash now based on that AA.
tl;dr: what's your post-FIRE investment/withdrawal plan? Execute that.