Happiness, rebirth, and the death of an arahant
Your question seems very sensible. Some thoughts... 

I think you're wrong to suggest that the Buddha was 'not sure what will happen...'. There are some things that may be known but not explained. He advises us not to worry about metaphysical problems and just take the medicine, but this does not mean these problems are not understood or the facts not known. 

If you are having a pleasant time, as you say, then you may not feel you are suffering and you may question the need for the medicine and have little motivation to take it. The Buddha was in this position early on but saw the suffering of others and recognised his own future death and suffering. His medicine is not just a cure for suffering now but forever, and while you may feel free of suffering right now this situation is not going to last. (Sorry about that).            

Thus it is said that the Gods have such a cushy time they may lose their motivation to push on to full attainment, but in the end even they must give up the pleasant life and sink back into the mundane, making it more helpful to be a human being with the motivation to go all the way.   

I doubt your pleasant situation will hold you back since it won't last for long. What you call happiness is not what the arahant means by the word. His or her happiness is unshakable and not dependent on conditions. When you are happy in a way you know nobody and nothing can diminish or destroy then you're properly happy. Usually our happiness can be destroyed instantly by a death in the family, an illness or even just a missed meal. Happiness is real happiness when it is permanent, at which point the word 'happiness' may become slightly misleading as a description. 

It's a slippery and subtle doctrine and these issue take some time to sort out, and they cannot be properly sorted out without some 'empirical' evidence to inform the process. 

Needless to say this is just some thoughts, not advice from a guru.