In what cases if any, does a transaction get lost from the network forever?

Question

Is it possible for a transaction that was included in the pending pool across multiple nodes, to become lost from the network forever (i.e. get dropped by all nodes)?

If yes, in what cases is that possible?

P.S. There are a few similar questions but with seemingly conflicting answers. Some say that transactions cannot be dropped from the network (e.g. What happens to transactions in Uncles?), and others say that it is indeed possible for a transaction to get dropped by the network (e.g. What happens to transactions in orphaned/forked blocks?).

Answer 1

Yes. But the exact circumstances are hard to pin down as it varies between nodes.

Each node on the Ethereum network will maintain it's own finite list of pending transactions. This is configurable on a per-node basis. Since the list is of finite size, if enough new pending transactions are received on the node or from other nodes, some transactions are going to be removed from the list permanently. The exact criteria for this are complex, but generally speaking it'll tend to be pending transactions with lower gwei.

If this happens on all nodes, your pending transaction is effectively gone.

More information can be found here