Recently I have been thinking about doing MS. For most of the universities, the admission is based on GRE General score among other things. I think a few letters of recommendation are a must in admission in almost all of the universities. I have been in employment in corporate sector for a few years now and the mentors (two of them) under whom I had done my projects/research in the university have left the university now and moved somewhere else. Will I still be able to get admission in MS without an academic letter of recommendation or with an employer's/colleagues' letter of recommendation?
I doubt that any place in the US with competitive admissions will admit a student based only on GRE general test scores. In fact, that is starting to disappear as a requirement (COVID among other things).
There are places that will accept nearly all applicants, but that may not be your goal. For the most part letters of recommendation rank fairly highly in the analysis of graduate applications in the US.
Admissions are generally broad based, with GPA, letters, your own statement of purpose, etc. being considered as a whole looking for indicators of success. If any piece is missing, the others become more important to the analysis unless the process requires the missing piece.
Academic letters are best for academic programs, of course, and you may be able to get one or two if you are remembered at your former university and/or by former mentors, or can re-establish contact there. Letters from employers might be fine, depending on the program and what your employment was.
But presenting no letters at all would probably indicate a weak application in most cases. Not having any academic letters is a negative, though perhaps not fatal if other things strongly indicate success.