There are many guitar tube amplifiers schematics that don't use negative feedback.
I was wondering how the negative feedback can help in the life cycle of the tubes? (If can help)
Voltage negative feedback with valve amplifier is here mostly to enhance the bandwidth, reduce distorsion and the output impedance. If this is desirable in the hifi world, it has less important in a guitar amplifier where distorsion is wanted and 50Hz-15kHz is common bandwidth. Furthermore, if on the paper negative feedback has only advantages exchanging gain for stability, in the reality, it kills spontaneousness this is why it is often presented as an option in a guitar amplifier.
So no, negative feedback has nothing to do with valve serviceable life. Heater voltage and respect of the DS values are by far more important.
No, whether a vacuum tube is used in a used in a circuit with negative feedback around it or not has no direct bearing on the tube's service life. As long as the tube isn't abused, it should be fine. It may be easier to design a circuit with feedback to guarantee it runs the tubes within some parameters, but that is just one more thing to take into account when designing a circuit without feedback.
The primary cause of tube failure, barring outright physical damage, is cathode wear. The cathode has a special coating on it to reduce the work function. This allows for reasonable cathode currents at lower temperatures than otherwise. However, this coating is degraded over time, especially as electrons leave the surface of the cathode. Very roughly, each cathode coating is good for some number of total coulombs, although there is a lot more to it than that. Feeback or no feedback doesn't by itself indicate higher or lower average cathode current. Usually these tubes are biased at recommended operating points, so both types of circuits would probably have about the same average cathode current.