Articling students can work remotely as long as they are still being supervised. Supervision of an articling student who is working remotely could take the form of daily telephone calls to check-in, videoconferencing, increased email communication, use of SharePoint sites to review work product, etc.
There should be a plan between the student and principal about how to communicate should the student need help and they are not in the office. Consider having backup contact information for another active lawyer that a student can reach out to for assistance in the event a principal becomes ill or is not available. As long as supervision occurs (remote or otherwise,) the student would still be considered to be articling.
For those sent home who will not be supervised, this could be a break in the articling term - a leave of absence. You will need to advise the Law Society if you have a break in your articles. Students will still be expected to meet the requirements of 12 months of articling plus complete the PREP Program.
If a principal gives a student time off for vacation or medical leave in the normal course of their employment (i.e. not months, but perhaps a few weeks), then this may not impact their articling term. For example, some firms routinely give all employees two weeks holidays and we have not considered this to impact the 12 months of articling time. We rely on the principal to confirm the articling term has been met.