Sure, there's a 'spiritual baptism' with-in Christ,...a co-participation in Christ that a believer takes part in,...but having a water baptism as a part of one's conversion experience is wonderful too, as an outward expression of faith.
If we hold to TULIP,....one's religious life may be somewhat indeterminable, except that one may suspect that his own 'free will' desires and efforts to love and follow God, are God-inspired,...but they may also be his own choosing too, as these often get confused. - in any case,...there is a 'co-operation' of wills...being 'married', but this is assumed to operate under different conditions per what school of thought you hold to (calvin, arminius, etc.). As all distinctions and duality fades into divine ground of non-duality (primordial oneness), of course...there is only the divine will triumphing, since it holds preeminence. In the divine marriage of soul and Spirit, there is only 'God' all radiant, in his omnipresence, in his totality...indivsible.
It must become disconcerting for a Calvinist who has back-slidden or fallen away from the faith, as he may suspect his initial 'drawing' was his own 'free will' and not God wooing him. Hmmmmm. But who know, what if a back-slider goes back and forth many times,...who knows who is at work,.....God or himself....OR maybe both?
As far as track-records of any Calvinist who did leave the faith, I dont know the %, but there a number of 'christians' who do leave for another religious path or more agnostic or atheistic view. Its pretty much a roll of the dice as far as calvinists go, unless they assume that by their own faithfulness, loving service to God, that He is continuing to inspire them, making them persevere...but I dont know what can be said for those who dissent from the faith,...again, it seems like a 'toss-up', because after all,...God will keep you in the faith to the end,.....OR you were never chosen to endure to the end to be saved, as God has already PASSED OVER you. For those 'passed over',...it doesnt really matter what they will or desire, since apparently they cannot undo the decree of God over them, and CHOOSE to REPENT, to return to God and be saved. The whole system is a travesty against man's freedom, while assuming 'God' has TOTAL CONTROL over sentient beings. - this is wonderful for the 'elect', but the 'unsaved' get a 'bum-wrap', and an eternal one at that. What goes on in the afterlife is also pretty speculative apart from some visionary imagery in a few passages of scripture, but for those interested there is much information on 'near death experiences', 'the afterlife' and spirit-communications...which gives us modern day current information of the after-life realms.