Every rail system does contingency planning for how people will get around if some or all of the rail line is shut down. These plans typically go through a range of likely cases, from closure of short segments to closure of the whole line. The typical response is to deploy buses to shuttle people between the closed stations. If the rail operator is not also the bus operator, then standing contracts with bus operators are put in place, to be drawn upon as needed.
A planner for a new light rail system would like to see examples of these contingency plan documents from major light rail or tram operators. If you have your agency's plan handy, please post a link to it in the comments. If it's not online, then send it to me in an email and I'll send it on, noting any confidentialities that you specify