Lost Buddies and Safe Ascent Procedures
We are usually instructed to look high and low for your buddy, spin in a 360-degree pattern and make absolutely sure they are nowhere in sight. Then, as a last result, return to the surface and hopefully you'll reunite. However, articles and the textbook instructions keep telling us to make a slow ascent to the surface to find them, but they never mention safety stops while completing this procedure.
So do you make a safety stop while trying to locate a lost buddy at the surface or not? Will we put ourselves at risk of decompression illness if we skip the safety stop? Is it correct to go straight to the top with no safety stop? And if we do go straight to the surface to locate our buddy, should we both re-descend and make a delayed safety stop to lower the DCI risk? I feel like this is a very valid question because I do want to help any lost buddy, but I don't want to seriously injure myself in the process. I can see this being of little concern in shallow depth, say 30 feet, but what if we are at 100 feet?
This is an excellent question and you seem to have raised all the salient issues. First, as always, your safety is always paramount, even to that of your buddy's. Certainly, you want to be a responsible buddy, but that doesn't mean you should put yourself at risk to relocate an errant buddy. Regardless of why you have to ascend, an ascent is an ascent. So, except in an emergency, the same rules and recommendations apply.
As you note, given the relatively mild decompression stress, I'd have no qualms about ascending slowly but immediately from a shallow depth -- say 30 feet or less -- without a safety stop. However, in my opinion, anything deeper should involve a stop, even if the reason for surfacing involves a lost buddy procedure. The laws of physics are not suspended just because you need to find your buddy, so the risk of decompression sickness is no less.
You also raise an interesting question about returning to depth to perform a safety stop after you've surfaced to reunite with your buddy (who hopefully has surfaced as well). The idea of "making up" a missed stop was probably inspired by a procedure used by the U.S. Navy (and once taught in recreational scuba courses) for what was termed an "omitted decompression stop." The consensus today is that there's little benefit to returning for a "do over." By then, whatever bubble formation has occurred, if any, won't be rectified by going back a second time. The idea is to not omit the stop in the first place.
Your question demonstrates that buddy separation can be a very significant issue, aside from the problems incurred by diving alone. If buddies must return to the surface to reunite, it may increase their decom-pression risk; so the answer is to make sure it doesn't happen by remaining attentive to each other throughout the dive.