They could communicate out via a buoy and really long cable, and in fact that is how a lot of scientific expeditions work. They communicate with a support vesse

They could communicate out via a buoy and really long cable, and in fact that is how a lot of scientific expeditions work. They communicate with a support vessel via cable. However, once the "wreck factor" is introduced all bets are off. Underwater objects being extremely difficult to locate is kind of why they are popular with militaries. "It was near the titanic at X time and date" is probably the best data you can ever hope for, and that's covered by the dive plan, no tech needed.