What is the ruling on the vow, "My Lord, I have vowed myself to You," intended for the purpose of learning and teaching Fiqh without compensation, without the intention of a conventional vow? And is it obligatory to fulfill it if the means to study Fiqh are unavailable? And what are the consequences of not fulfilling it upon death?

A vow is established by any statement that implies commitment. Your statement, "My Lord, I have vowed myself to You," is an explicit form of a vow and does not require an intention. Since you intended by it to acquire knowledge and teach it for free, this is among acts of obedience and closeness to Allah. Therefore, it constitutes a binding vow according to most scholars, and you are obligated to fulfill it. If you are temporarily unable to fulfill it, then wait until you are able. If the inability is permanent, then you must offer an expiation for breaking an oath. If death overtakes you, there is no sin upon you.