Had stents put in for kindey stone been 8 months what will happen if not removed?

There are various possibilities including nothing, it may predispose to urinary tract infection; or you may want to go back to the information sheet and explanation given you by the urologist. I hope you know the type of stone you had so you could adjust your nutrition to reduce chances of future re occurence of kidney stones.

It needs to be removed as soon as possible for avoiding complications such as infection, bleeding, broken stent when removed when it is in place too long, chronic irritation to the ureter and bladder may precipitate unwanted outcome for people at risk, etc.

That is a bad scenario. calcium and other components of urine get deposited inside and outside the stents and block it as it is a foreign body and make it very difficult to remove. stents if placed for long yerm are changed at least every12 weeks or so. So if it is *8 months pl see your Urologist NOW