It depends on the situation. If the buddy were observed drifting away by the boat crew and they knew they would need to go down current to pick him up later AND if the buddy were not self sufficient enough to do ok on his/her own, I go with the buddy.
If the boat crew does not spot you, they would be short of information on when the two of you surfaced and missed the line and will probably delay for a significant period of time waiting for you to surface. At the point, they determine your gas is exhausted, they still won't know if the two of you are dead on the bottom or if you surfaced, when you surfaced or where you surfaced. The increased time before the search starts and the and uncertainty of if, when and where you may have surfaced will greatly expand the search area and will further delay any rescue.
If your buddy is self sufficient, has proper signalling devices and is not going to panic, there is no need for you to go with him or her. All going with the buddy will do is create another potential victim and deny info and resources to the boat crew. And if the seas are rough, weather is foggy etc, there is no guarentee of a quick rescue for either of you and the job will get twice as complicated if the two of you are separated later before you are rescued.
"Never leave your wingman" is overly dramatic and is also a very poor analogy as it only applies until he flames out. At that point you can be in tight formation 3 ft off his wingtip and there is not a thing in the world you can do for him as he is going down one way or the other. (Well...not counting the F-80 pilot over Korea who stuck his nose up the tailpipe of his wingman's flamed out F-80 and pushed him south out of North Korea and practically to the traffic pattern of an air field.) Two pilots punching out instead of one accomplishes absolutely nothing except creating two pilots that must be rescued and denying your wingman a potential CAP while he waits for the SAR folks to arrive. Similarly, in most cases you'd serve your buddy far better on the boat than you would in the water.