>>40775644In the grand majority of sunni schools of interpretation, abstaining from prayer automatically renders you a kaffir and banishes you from receiving God's mercy in the afterlife, unless He decides otherwise for one reason or another (which is unlikely). In the days of the caliphate, those who were not praying were tried and punished for heresy if they were adamant about their choices, and would not be get the proper muslim funerary service once they have passed away, as in muslims won't pray for their ''salvation'' and such, and in the most extreme of cases, won't even get buried in a muslim cemetery.
I don't know if the shias, particularly in Twelverism, are as strict about this issue. I do know that they their schools of interpretation have very varied understandings of how to prayer, including how many times it must be done on a daily basis, due to their dismissal of the regular Hadith corpus.