Of course Neither Naruto or Sasuke can just using their powers. However both Naruto and Sasuke combining their powers to save Obito using their yin and yang marks could save Obito. Hell I believe it could even stop someone from certain death until he/She was not dead.
However I believe that without will to keep living even god power can not force you live. In other words I believe Naruto and Sasuke attempt to stop Obito from dying but he will accept death and refuse to stay alive so their marks won't work. It would be amazing if it happen, just like in my prediction, check it below:
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