No, lines following a line ending in a colon must be indented.
But the OP's point is that you can't know how many lines make up the indented block, since there is no explicit block-end-marker left if the indent is gone.
But the OP's point is that you can't know how many lines make up the indented block, since there is no explicit block-end-marker left if the indent is gone.
Except if you have, for example, an if statement. if x: y() is valid.