Non-upgraded node (eg. merchant selling goods) would see and accept such transaction as valid (and send goods to customer).
All miners will upgrade software, otherwise they will mine block which will be rejected by majority.
So, this transaction will be unconfirmed for this merchant.
But I recommend you to upgrade your wallet!
So waiting for at least one confirmation (if all miner upgrade) and 2-3 confirmations if majority upgrade. OR Upgrading wallet.
Exactly those two solutions I excluded and did not ask for.
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(besides upgrading node to include segwit and besides waiting for several confirmations for all anyone-can-spend scripts)