Without any accusations, tell him the path where you‘re heading in written form. You can add potential remedies and the end, but in essence, describe what will or might happen.
A good phrase in these kind of messages is
“Unfortunately you didn’t have time to look into XYZ. I’m truly sorry that we now face ABC. But if we do EFG we might still have a chance in fixing this”
In general: use written form, avoid any phrases that put the blame on him, describe accurately what happened and the consequences and end on a hopeful note or idea.
“Unfortunately you didn’t have time to look into XYZ. I’m truly sorry that we now face ABC. But if we do EFG we might still have a chance in fixing this”
In general: use written form, avoid any phrases that put the blame on him, describe accurately what happened and the consequences and end on a hopeful note or idea.