what happens to low-fee or forgotten transactions
Likely the transaction will be kicked out of the pool - purging it from the node's &quot;memory&quot;. Its hard to imagine that there would be a transaction that would qualify for that treatment with one node, but not for others.
But anything is possible.
If that were the case, then that transaction would just remain hanging in the mempool for that particular node that decided to keep it (for whatever reason). For this portion of the protocol though, its more important to take into consideration which action the network would take overall.
How That Specific Node May Handle Things

There's a chance you may attempt to send a duplicate transaction (from the perspective of that node), unwittingly.

Unless you had the RBF flagged ticked for your TX (which there's a good chance that you may have since this is default Electrum behavior along with many other wallets), the node will reject that new transaction attempt since its likely coming a million years after you sent the initial one

Assuming most of the network purged that TX though (they probably did), however that node decides to handle your re-broadcasted TX (if you do that), is neither here nor there