While overboost protection is lost in alternate mode, I had thought at the time that there was still overtemp protection for the engine but it appears that this is not the case in alternate mode. Only overspeed protection at all times and overtemp protection during start. Please correct me if this statement is wrong.
I am not sure of the price of one of these engines but obviously, there is some concern about what might have happened.
Boeing design philosophy is, autostart aside, there is no automatic protection against EGT exceedances, even in Normal mode (overspeed is different - protection is always there, including a mechanical backup for N2 on the GE90). That's because we don't know why there is an EGT overtemp - it might be because you lost the other engine and you need that last bit of thrust to clear an obstacle, or because the EGT harness is shorting and the EGT indication is bad. That last part actually was a problem when we briefly did have EGT limiting on the 767 - the Pratt engines had crappy EGT harnesses and the EEC was unilaterally limiting thrust during takeoff due to erroneous EGT indications - hence the reason Boeing decided that was a bad idea.
In addition to turning the gauge red, EICAS automatically records any exceedance, it's a simple matter to pull up the max temp and time over redline. There is a handy chart in the Maintenance Manual it tells you what action is necessary based on the max temp and time.
Last I heard (which was a while ago), new GE90 engines were going for about $12 million. But an overhaul is usually 'only' a million or two
