The definition of heaven can be explained by means of an example. Consider heaven to be a hotel (restaurant). Like, in India, a rich man in summers goes to cold places in cities like Simla or Kullu Manali. There he stays in a hotel in which the room rent and the food-expenses have to be paid. After spending a hefty amount in two or three months during his vacation, he has to then return to his sphere of actions. Then he is back doing hard labour for the rest of the year. The same thing happens in subsequent years i.e.spend your own earnings for couple of weeks or months and then return home. If however in some year, the earnings are not good, then even may have to suffer for the want of that comfort of two months.
Consider heaven to be similar: - After doing worship on this Earth, one goes to heaven-like hotel for some time. Then after spending one's virtuous earnings, one has to again suffer in hell and in the bodies of the 84 lakh life forms on the basis of the sinful deeds.
Until one will find a Tatvdarshi saint, the sufferings in the above mentioned birth-death, heaven-hell and 84 lakh births of various living beings will continue because only the 'Satnaam' and the 'Saarnaam' of the Supreme God destroys the sins. The sins are not destroyed by the worship of other gods. One only gets the predestined fruits of all the deeds.
Therefore in Gita Adhyay 8 Shlok 16, it is said that upto Brahmlok (Mahaswarg / the Great Heaven) all the loks are destructible. When even Heaven-Great Heaven will not remain, then where will the worshipper find refuge; please think.