Cracked Exhaust manifold

[marks_C]

my polo 6 hit the top and to fix it is R19, 20o. Im told that the exhaust manifold still has to be fixed as it is leaking but its no big deal---it will only lead to fuel inefficiency. Huh? Should i give them a go-ahead and fix and then deal with the exhaust manifold later? I am car less and it sounds too technical.
help.