Well I tried "bitcoin-qt -rescan". It went from 1 % to 100% in 10 minutes or so. Not bad at all. But ...
Let me guess: you're running it from an SSD? It takes my PC 2 hours!
My new wallet has had an total activity of 3 Transaction. First two where transferring the old wallet balance. The third transaction was a test transaction of sending 0.05 BTC to a friends wallet.
The third transaction has 0 confirmations, it was offered to the network with a fee of 0.00000224 BTC. Obviously i was to greedy, because from 20 december up to now (28th of dec) nobody put it in a new blockchain. The transaction id of the third transaction can't be found anymore on Blockchain.info so i guess it is officially dead now.
I'd say try the zap-thing:
bitcoin-qt -zapwallettxes
That will also get rid of your unconfirmed transactions in your wallet, if it's also dropped from mempool you can make it again.
My available balance is 0.0002 BTC (my pending balance is still 2.

. Should i try to send my last available balance to get the third TX afloat ? Silently hoping that this will get al of my pending total back to available, or is it something else?
It's a different input and has nothing to do with RBF.
If the zap-thing doesn't work, next step is to export your private key. Since you have the 0.0002, your wallet should have the private key to the 2.9 at the same address. I kinda expect the zap-thing to work, but if it doesn't, the next step would be to export your private key and import or sweep it into Electrum.