The O's slim top-six hopes came to an end despite a 1-0 win at Coventry on Saturday, but victory over Oldham next weekend will ensure they finish a creditable seventh.
Orient lost their first three matches of the season but Slade refused to dwell on what might have been.
"Every club will have its own tale of woe," he said.
"Ifs, whys and buts will haunt people but it's gone, you can't do anything about it, you can only control the future
"If we can keep the nucleus of this squad together going forward then I'm sure we can be very competitive in League One again next season."