Hi!
The first childhood guinea pig in my life lived to nearly 10 years back in the seventies; but a fair number of my (adopted) piggies have lived to 7 and 8 years old and one old lady (who came here aged 7 to live out her life in piggy company) even lived to celebrate her 9th birthday. I know of the odd piggy living to 10 years and very rarely beyond.
The average healthy life span is about 5-7 years, so be proud that you have got your piggy that far, first and foremost!
However, you can never count on for how long your piggies live and what they ultimately die from. It can happen right of the blue and very quickly at any age. There is never a guarantee and fairness doesn't come into it.
The best way to approach your fear of loss is to see your pets as on loan from above on a contract that can be withdrawn anytime without warning. Turn your piggy's life clock back to zero and see every day more as a special blessing which you consciously appreciate. This way you do not waste the remaining time fretting and waiting for the inevatible end but you fill it with lots of love, fun and enrichment so you do not have to deal with lots of regrets on top of the pain of the loss. Guinea pigs don't have a concept for average life expectancy; they measure their lives in happy todays. If you try to do it the piggy way, you still have plenty of time to create precious memories that will warm your heart in dark hours years down the line and that bring a smile to your face when nothing else will. You can put a lifetime's worth of love in just a moment but you can fritter away years with fearing what you cannot stave off.
Enrichment Ideas for Guinea Pigs
The Rainbow Bridge piggy that brings a big smile to my face whenever I think of him is my Bryn Oscar (the name deaf) as he simply proceeded to do what he loved and wanted doing. He was a five years old widowed neutered boar who had found no interest, so he came here to live with my lady pensioners in a new group. He was here for only a year but he clearly had a the time of his life and enjoyed himself so much (including several escapes and taunting the other younger husboars through the bars) that when he died age 6 that one year felt truly like so much longer - and he has left me with so many happy memories. Time is relative; it is not a measure but what you fill it with.
PS: Please always put your piggy's welfare before your own fears of loss when you come to the sharp end. However much you fear it, you can always be strong for one you love where you can't be for yourself.