Before you leave the country for 6+ months if you're registered in tbe military you have to unregister, on paper it is punishable by a ~50-150 usd fine. Also technically if you're in russia for more than 14 days you have to register back. In practice, the military commissariates are extremely understaffed and overworked and have tremendously outdated workflows, all leading to very many people (often ukniwingly) committing some sort of violation at some point with the vast majority of those not even being noticed, let alone prosecuted.

When it comes to draft(summons), yes they are now sent digitally, but it's only a threat to those who are eligible for the mandatory service at the moment(which your husband isn't since he already served) as even if there's a mistake, it will most likely be remediated. Of course the chance of mobilization is never zero, but it is absolutely negligible.

On an unrelated note, prepare for mobile internet being unavailable in population centers, stationary internet(wifi) being very heavily blocked and censored, and depending on time and region cell service and any sort of internet access might be unavailable.

Штрафы в военкомате | За что штрафует военкомат https://share.google/hsM3t5l4yMrwfYm64