Think another posted but I have had the same issue, I've lost my companions after coming out of Lucky 38. I've looked all over New Vegas and I cant find them. The game also wont let me get any other companions to fill their spots. The build I made my chara, really counted on the companions I had to work without having to adjust the game to easy or very easy just to survive the rest of it, after 22 hours of play time this really a heart breaker.

Is there any way to fix the issue, or do I have to start the game over because my chara can't handle it on her own ?

What I did was this : For Starters I retraced my steps to see if I could find my lost companion (Boone) to No AVAIL... (I'm not giving up that easy). NEXT : I went to a safe area (no enemys) outside of the actual New Vegas Strip area, I went to FreeSide, you could actually just about go anywhere that you are accepted or idolized ...(I'm Neutral @FreeSide )... To prevent complications I went ahead and saved my progress at this point...)
....LAST: To regain my follower (Boone) I waited for 3 days in game (wait 24 hours, then wait 24 more hours and again wait the final 24 hours) then the game made my follower leave my party and return to their place of origin Display "Boone has Returned To Novac" ... SICK (with Boone he was his hotel room, @Novac from 9am - 9pm, dinky the dinosaurs mouth from 9pm-9am, he works nights ) ...

NOTE : No way to be sure if this will work for you if your having a ton of crash or bug issues. I do not run my PS3 all day everyday (DO NOT) play New Vegas while on the Playstaion Network your PS3 will experience more issues if you are online so I turn the internet on my PS3 off, I have also turned off the auto save feature in New Vegas due to years of playing Bethesda Teams games I know to SAVE OFTEN (I try and save every 15 mins) and I also use 2 save slots one for my main save and one for a backup...if you have the memory to do so.... Just in case you run into an error, then you have a backup! I run a backup copy save (save slot 2) every 35-40 mins of gave play Real Time ....

to long, to obnoxious in colors did not read

Thanks SickSkinInk! I knew my companion left after a while but I didn't know the exact amount of time it would take.