If an airline cannot get you to where you are supposed to go, they are supposed to get you there as soon as possible, most major trunk carriers have interline agreements with one another, which is what everyone alive is referring to. Now when it comes to rebooking you on another carrier all airlines will try and keep you with them, and every carrier has its own particularities. If a BA flight is canceled the day before, BA will give you dozens of options online and try to not do things in the phone, but if you does up at the airport, they will generally put you on what you want. EK is the worst and you really have to fight for authorization. Airlines line Delta, Lufthansa and Air France are fairly laid back in my experience. TK is somewhat in between, and that has to do with the corporate culture, in an irrops situation at IST you are going to be seen by TGS people, who generally do NOT have the authority to FIM into another carrier, a TK manager generally has to sign off.... And they are sometimes intentionally hard to find... Even if you are flying in paid biz, even if you are E+.