Mariner told BBC Spotlight: "We thought we could get out of this situation, but we've come up a little short.
"If anybody knows me they know I've only ever been associated with success. I'm a winner and now we've got to start to rebuild for the future."
Monday's result ended Argyle's six-year stay in the second tier of English football, with Sheffield Wednesday and Crystal Palace's final-day encounter meaning it is impossible for them to stay up.
Plymouth have won just 11 matches in a season which has brought many more lows than highs.
Mariner said: "I feel the pain of the supporters because this is the club that gave me my first start.
"The reason I came here was because of the vision that the club can get into the Premiership.
"Now we've got another couple of hurdles before we do that but I firmly believe that we can do it."
My question is - what next?
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With two Championship games still remaining for the Pilgrims to see out, Mariner said he would endeavour to make sure the club finish the season on a high. "We need to go to [Nottingham] Forest and win, and Peterborough need to come here and we need to beat them," he added.
"We need to finish off on a high to show our fans that we are determined to bounce back."
And signalling his intention to stay and bring Championship football back to Devon, the 56-year-old said: "We obviously need to look at the staff and we need to address certain situations, hopefully I'll be asked to do that. I want to do it."
Source: BBC Sport
Source: BBC Sport