I've talked to the new owners of Sig at Toledo this year and I can tell you first hand that there is very little chance of Sig going under or being purchased by Horizon or Hobbico buying them out. The new owners are totally committed to making Sig one of the top companies in the RC industry. They have been working hard at restoring both their ARF and kit offerings and have plans to bring out lots of new planes as they move forward.
With that said I will say that I've built plenty of Sig kits myself over the years. I have 3 Hog Bipes, 3 Something Extra's, a 4-Star 60, a 4-Star 120, 2 Sig Wonders, and several others that I can't think of of the top of my head. They are a great company that produces great kits.