Bar end shifters, except for a broken cable, just about cannot fail because they all offer a friction option. BTW, bar end front shifting is always friction. None I'm aware of offer indexing in front.
That said, I believe the worry about STI failure is more of an academic exercise than a real problem. I had a pair of 105 8-speed shifters last over 28,000 miles and I replaced them because the shifting was getting sticky, not because of sudden failure. Their replacements have 22,000 miles on them and still work perfectly. My son-in-law got over 25,000 miles on 8-speed 105's and replaced them only because he wanted to upgrade to 9-speed. My son has 15,000+ miles on a set of RSX levers (Shmano's lowest line STI)and they are still working fine.
Anyway, my point is STI shifters are quite durable and failure of another major component is at least as likely to strand you.
I might consider bar end or downtube shifters if I was going to tour WAY off the beaten track but for anywhere in the US or Western Europe I would always have the convenience of STI.