No you dont, it will still get updated on itch a few days after the steam launch.
If there will be further updates beyond that all depends on how it goes, i truly believe when people see FlowScape they will love to buy it, but if sales numbers are too low on day one, steam may not put it on their front page. If you want to see development continue, you would indirectly help by wishlisting it and buying a copy for yourself or a friend.
<3
