I recently learned a little bit on offering and doing the long life puja (Kandro Tenshug).
I was told that if the guru does not appear and accept the puja, the puja will be of no use in prolonging your guru's life, the intended purpose would not be fulfilled - only merits will be generated in doing the puja, like performing any other puja. But if your guru accepts the offer of the puja, it becomes very powerful, as that would mean that he will live longer to continue turning the wheel of Dharma. Highly attained lamas have full control over their birth and death, and therefore, if accepted he can extend his life - is what I'm saying correct?
Anyways, I agree with whitelion. If we do not create the causes for our guru to stay by transforming our minds and doing more, going allt he way, then ultimately it makes sense for the guru to leave us, as he can go somewhere else to benefit others who are willing to transform. Maybe it's a method of teaching, that when we become complacent and our guru leaves us, then we only will regret and it will push us to do more?
There is so much love and care given to us by our guru, and if we reciprocate the same, I am sure that our guru will remain to teach and guide us. But if we take things for granted then what is the point? We abuse the compassion, kindness and love - so we push our guru further away.
I am very excited and happy that Geshe Lobsang Tenzin accepted his students request for a long life, continuing to spread Dorje Shugden, the Dharma, and allowing his students to serve him. May I have the utmost merits to visit Shar Gaden one day, to meet this esteemed lama.