

In most multiparty systems, a party needs to hold a certain number of seats in Parliament in order to be in power. If no party has enough seats after an election, they attempt to form coalitions in order to get enough seats and form a government.
A party leaving the coalition means that it’ll no longer hold enough seats to have a majority. I dont know the specifics here, but they might be able to form a coalition with a different party, or require new elections.
Canada has first-past-the-post voting and still resulted in a minority government this year.