Seiya is definitely worth 9 figures in the open market, IMO. Can the Cubs afford to lose a 130+ WRC+ right handed bat from the lineup? They could go years without finding a replacement that could do that.
5 years 110 mill seems like a fair offer, from my perspective. They've kept Happ around for 10+ years on a similar AAV. I'll be really disappointed if they let a much better player walk over a couple million