Harriet Harman resigned the Deputy Leader position following this year's election, although she's been acting as Leader of the party since then until Saturday. I think she's been looking to step back from front-line politics for a while, and would be nowhere near the Shadow cabinet whoever won on Saturday (ie she's not part of the group of Labour MPs choosing backbench life over working for Corbyn).
And Dennis Skinner is now over 80 years old and perhaps not interested in/ lacks the energy for front-line politics.