If Die Linke were to fail the threshold but get the 3 seats, the party would still face harder times. In that case, the party would only form a "Gruppe" instead of a "Fraktion", basically a parliamentary caucus with less rights and reduced funding, meaning not only lots of its MPs would become unemployed, but also large parts of the party's parliamentary staff.
If they miss the 5% just barely, Die Linke could still get 5% or more of the seats in the Bundestag and be considered a Fraktion.
Also this rule is only codified in the Geschäftsordnung (
"rules of procedure"?) of the Bundestag and could be changed quite easily if Die Linke would take part in a coalition for example.
Still wouldn't be good for Die Linke to miss the treshold though.