Fr. Seraphim did not discuss the issue of who has or has not grace. He spoke of apostasy and renovationism. If Fr. Seraphim can make it to heaven without arguing about grace, then I think we can, too.
First of all, know this background: that basically the policy in ROCOR is not to commune new calendarists. But, and this is a big but, most bishops will give many of their priests the right to take each case individually. It is the priest who has to answer to God for any misuse of the Mysteries. The priest has a duty to each soul, and a duty to God at the same time. In each circumstance the priest needs to discern if withholding the Mysteries will unnecessarily deprive the soul, or if administering Communion will harm the soul.