There's no reason you couldn't run the Sig alone. My Sig 10k's actually came with a tempest weather flow wind meter if you wanted to go that route you don't even have to buy one separately.Would the Sig work by itself for you? You use the sig just for yardage? For hunting would you still use kestral? What about a cheap windmeter and using sig for firing solution?
Personally I'll still carry the Kestrel since it's not big or heavy but you do bring up a good point that the main use for me is multiple target engagements and use the Sig to push yardage info to the Kestrel mainly for time savings.