The 737NG is certified for one engine out approaches and landings with Flaps 30 up to CAT IIIa. So why change anything when experiencing an engine failure during short final?
Stay at 30 if you have that, consider changing to 30 if you have flaps 40 however do not unstabilize your approach by needless activity. If you have to go around out of flaps 30 just use the normal go-around flap schedule (15, at acceleration height 5, 1, up).