What to do if separated should have been discussed prior to the dive.
The standard recreational procedure is to surface after 1 minute, but that is not always optimum. I learned to dive in low viz and high current and the odds are you will get separated during the dive. Staying together as a buddy team is nice in theory, but not alwas in practice if it requires several "bounce dives" during the course of the dive or creates other navigational or safety issues. So you have to weigh the pros and cons. In many cases the current on the bottom is much slower than the current mid water or at the surface, so bouncing up and down, to rejoin during the dive in addition to decompression/sawtooth dive profile issues, will speed yopur drift rate and separate you farther from other teams who may be exiting at the same time or point, complicating the pickup or exit timing.
Realistically, unless you are staying right on someone's elbow 100% of the time, staying together in low viz/high current is problematic. A buddy line may be an option, but it may also give you 6 feet of strap between the two of you to snag on submerged obects and tie you both up.
Realistically, if someone has an issue it is often gas related and they do not have the rime to cover any distance that will result if they stop and the buddies continue, or that will occur if they drift up off the bottoms. Alternatively if they get hung up on fish line, etc, there is not much a buddy could do to get back up current anyway so in effect if something happens, a diver in a buddy team in a low viz high current sitation is very likely to be on their own in an emergency anyway. Many will argue that it is better to be honest and admit that up front so that you can tailor your dive plans and the aggressiveness of the dive accordingly. Those types of conditions are in my opinion an excellent argument for proper training and equipment for solo diving regardless of whether you dive in a buddy team or not.
Normally a 3 person team is not a big problem, but in those conditions keeping two people together is difficult and keeping three together is even harder, particularly if the tail end person cannot see the leader - a situation where lags in response times and lackof visual cues virtually ensure the third man will get separated if someoen stops, slows down, alters course suddenly, etc.
So discussion before the dive is important as a new versus experienced diver may look at the situation entirely differently. And if knowing that separation during the dive means staying separated is not ok with a diver in the group that diver can then:
1. opt out of the dive
2. devote the near total focus needed to stay in close formation with a buddy in a low viz, high current situation,
3. buddy with someone else who will follow the 1 minute rule and accept the risks involved in that approach, or
4. at least know that rejoining will not be attempted and not feel guilty for not searching for the missing buddy.