I had VSG in August 2017, and I've barely noticed any hair shedding and I haven't lost any locs. My edges may have thinned a wee bit, but not much. There were also some "mind games" I played with myself because I was deathly afraid of waking up one morning and seeing a loc on the pillow.
Maintained my locs as close to surgery date as possible --- since my scalp is most visible after rolling my locs, I figured I wouldn't be too freaked out to continue seeing it, THEN
Didn't do any maintenance until early December --- I didn't want to overmanipulate or handle my hair too much so I wouldn't lose (more) hair. And seeing new growth over the last four months balanced out any fears of hair loss.
Washed my hair the bare minimum necessary --- once again to decrease overmanipulating my locs. This turned out to be once a month and since I wasn't sweating, I could get by with a dry wash.
Wore my hair out or very loosely tied back
Like everyone has mentioned, MAKE YOUR PROTEIN GOALS! I made my own protein drinks with almond or cashew milk and added high quality protein powder and dried fruit. I added high quality collagen powder to my broths, soups, jello, pudding, whatever food I eat as long as it doesn't mess with the taste too much. Now, I'm able to swallow a biotin capsule without heaving so I take that as well.
Don't let the hair loss scare you; I know it's hard but it will grow back if you lose a little or a lot. What's the point have having beautiful locs when you have diabetes, heart disease, hypertension, or whatever weight related illness this surgery may help prevent!