McKillop's men still have fourth place in their sights after a last-ditch 25-21 win over Glasgow Hawks. However, with the posts at Goldenacre being taken down this week, they will meet the newly crowned Scottish Hydro Cup champions and current league title holders away from home.
Two tries by Marc Teague and a string of kicks from skipper Graham Wilson gave Heriot's an 18-16 lead with two minutes to play but Kerr Gossman added a last-minute try to an earlier touchdown by George Hunter and 11 points from Duncan Weir to edge Hawks ahead.
But Michael Maltman powered over in the last play to preserve Heriot's hopes of being involved in the British & Irish Cup again next season if, as rumoured, four teams are invited.
"It was a good result but the performance was a little bit disappointing," said McKillop, who will consider several options before deciding where to play the match against Ayr. It's going to be somewhere in Edinburgh. Edinburgh Accies, Boroughmuir and Currie have all kindly offered their pitches so we'll just see which one suits best."