Windshaper is a Unit.
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If a Flying unit can't fly due to an effect like Sandstorm Titan's, it will still get the +1/+1 as long as it still has Flying in its card text.
The +1/+1 bonus will not be applied to units that have been Silence (i)Silence:
Remove all text from a card and its attachments. and no longer have Flying in their card text.
Your Flying units will lose the bonus when Windshaper leaves play or is silenced. If the unit had 1 health prior to Windshaper leaving play, it will not go below 1 health when the ability stops.