How can one respond to someone who argues that God has not guided them as a justification for abandoning prayer?

The servant has a will, but it is subservient to the will of Allah, and one distinguishes between voluntary and involuntary actions. To use divine decree (qadar) as an excuse for abandoning acts of obedience, such as neglecting prayer, is a false argument. It is the argument of the polytheists and a satanic delusion. If it were a valid excuse for anyone committing a sin, it would have been valid for Iblis and Pharaoh. To use divine decree as an excuse for heinous acts and injustices is invalid by the consensus of all religious communities and people of intellect, because Allah does not command indecency nor is He pleased with disbelief for His servants. Rather, He has commanded obedience, both inwardly and outwardly, and forbidden disobedience.