I didn't see your earlier question, but have just looked at it now - this particular Euphorbia has bienniel stems, some flowering one year and others the next. The ones that have flowered should be cut down to the ground, leaving those that haven't. However, this particular variety dislikes excessive winter wet and cold, so you may well have lost them - and if you cut them down at the beginning of March or earlier, they may well have given up the ghost completely. If you're fed up waiting, and want to plant up, do it now, but otherwise, if you can give them another couple of weeks, till mid May, they may yet put out growth if they weren't completely dead when you cut them down.