Your car is designed to start in 2nd gear, unless KICKDown is activated, or the shifter is put into 2 at a stop. If you do a search under "first gear start" you'll find TOO much info on the topic... so there is no lack of info on this subject.
Your car was designed to safely operate just under the redline, at the maximum point before your engine falls apart.
MANY MANY things could happen... you'd really SCREW up the camshaft, you'd overheat the engine, warp the head, bend some pistons... a lot of MAJOR ***** would be endured on the engine! Don't worry about it.. because, good thing, YOU aren't able to do it. (Just don't put it into 2nd when cruising above 68 mph!!)
2006 E350 w/ 155k miles (Daily Driver)
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)