No one can tell you unless you say what unit it is...
Some units you have to complete ALL assessments to pass the unit
If you don't need to pass all units, still, not doing it would be stupid - it's worth 15%... so that leaves you with an absolute possible total of 85%...
Say something goes wrong and you fail one of the other assessments, or you get sick and can't do the exam, you'll liekly fail the unit..
Just do the assignment... if you have reasons for being unable to do it properly, apply for special consideration - it is NEVER better to just not do the assignment...