Life support means feeding tubes, intravenous drips, mechanical respiration, heart/lung bypass, urinary catheterisation and dialysis. Two main complications can occur: infections at the points where intravenous lines and drains enter the body, and the problems associated with long periods of immobility. In principle, there is no upper limit to surviving on life support.
Patricia LeBlack from Guyana has been on continuous kidney dialysis in London for 40 years and John Prestwich MBE died in 2006 at the age of 67, after 50 years in an iron lung. More invasive life support, such as heart/lung bypass, is only maintained for a few hours or days, but patients with artificial hearts have survived for as long as 512 days.
https://www.sciencefocus.com/the-human-body/how-long-can-you-be-kept-on-a-life-support-machine/
Need a pillow.