To retain a language it requires active usage. Swedish has zero utility outside school environment unless someones life is such it includes interaction in swedish. Most people I know are more fluent in english than in swedish. While I personally retain some rudimentary basics, when I need to talk to my swedish colleague, I use english.

To get MSc one must theoretically prove to be able to communicate in swedish but the minimum acceptable level - how to put it - is not very high.