The chain will break when you least expect it. You can buy it at McMaster-Carr if you can't find it locally. I always carry a spare too.
Edson recommends replacing every five years, IIRC. A little to often for my taste. OTOH I have broken mine at least three times in 25 years of ownership (over 125,000 sea miles). Went through St Georges cut in Bermuda on autopilot due to chain break.