Heldt had raised doubts about the coach's future at the end of the first half of the season, saying an in-depth analysis was first needed before any decisions were taken.
Schalke subsequently backed Keller over the Christmas break and, at the start of training ahead of the second half of the season, Heldt has once again given Keller his support, albeit on one condition.
"He's definitely staying as coach, at least that's the plan," Heldt said. "But if we lose 10 games in a row, then even I will lose my job. Everything would be torn apart if that happened."
Keller has had concerns about his future ever since he took charge of the club just over a year ago.
Even leading the club into the Champions League last summer did not see the doubts disappear, and Europe's leading club competition has probably saved him once again with their qualification for the last 16 putting their current league woes into the shade.
"The only way for us to end this discussion is by being successful," added Heldt, laying down the gauntlet to Keller to reduce the four-point deficit on fourth-placed Borussia Dortmund as soon as possible.
"We have set the bar high for the second half of the season and we want more points.
"We will try to reach our goal of qualifying for the Champions League once again, but it's not going to be so easy."