If Aubameyang isn't a crucial player for Chelsea, Chelsea management won't force them to sign Aubameyang on the last day of the transfer window. If you followed the issue on Chelsea squad, you must know that Chelsea was looking for a strong CF to be the replacement for Lukaku. Chelsea needs a pure CF to score more goals, Aubameyang is a perfect player to solve the crisis in Chelsea attacking line. Anyway, Havertz isn't a pure CF, so he has nothing to do with Aubameyang's position. Don't you understand that Havertz is an attacking midfielder?

Not matter with crucial player or not for Aubameyang but Chelsea doesn't have many alternative option after rejecting by many transfer player like Raphinha, Dembele and many other central forward. Chelsea not spent much money for Aubameyang and make this easy reach agreement deal with Barcelona depending Aubameyang have loss opportunity settle regular position after taking place by Lewandowski.
Waiting about Aubameyang performance with Chelsea to know he still crucial player or not, last season he has not really bad performance with Barcelona but have difficult level between Primer League and La Liga. Aubameyang have know well with Primer League competition ever joining with Arsenal last several season but right now he has different atmosphere with Chelsea.