While Smith has played regularly in recent weeks as cover for the injured Scott Fox, Slane has endured a frustrating spell at Firhill after penning a loan deal from Celtic.
Boss Jackie McNamara said: "Paul Slane will return to Celtic when his loan ends and Graeme Smith, too, looks set to leave when his contract expires after the Livingston game.
"In an ideal world I would like to keep Graeme but finance is obviously a major factor in that.
"He is an experienced keeper and has been really solid for us with his fitness getting better all the time.
"He really helped us out while we were going through a difficult time with injuries in his position."
McNamara has completed a deal to keep striker Steven Craig at Firhill for the remainder of the Jags' Irn-Bru First Division title challenge after he was released by Ross County while midfielder David Rowson has joined Second Division side Stenhousemuir on a month-long loan deal.
McNamara said: "I'm delighted to get Steven signed up until the end of the season.
"He's a good lad to have around the place and he's already scored some crucial goals for us both in the league and, of course, in the Ramsdens Cup semi-final.
"It was good to get everything settled so quickly. Steven is going to have a big part to play in the rest of the season."
Elsewhere, Hamilton have signed defender Jonathan Page on a deal until the end of the campaign following his release from Motherwell.
Accies manager Billy Reid said: "I am delighted to keep Jonathan here. We have been doing well recently and Jonathan has been a big part of that."