By 'leave' I mean have the utensil sitting in the pan for 10 minutes at a time while the food cooks.
By 'silicone' I mean "high temperature silicone" from a reputable manufacturer
By 'utensils' I mean spatulas, spoons and the like.
By 'safe', I mean
a) It won't melt
b) It won't cause health / flavour problems
By 'high heat cooking' I mean
a) As hot as an oven can get (In the UK, 500°F, 260°C, Gas Mark 9)
b) Cast iron cookware, past the seasoning smoke point, but before the seasoning is cooked off, for very fast searing of steak.