買輪到到期日都唔放會點?係咪一定會變廢紙?點解?

Not a must.
Depends the warrant is in-price or out of price, if out of price 一定會變廢紙.
But if in price , then it will
現金結算

大部份在香港上市的認股證均以現金結算，即到期時，持有人將不會收回股份現貨。在到期時，若投資者所持的認股證屬價內，發行人
將以現金付予投資者應收回之結算金額，款項將自動過戶予投資者的股票賬戶。

yes
if u hold to expire day, as market cannot trade it anymore, so =$0
but u can execute the call/ put warranty
call(buy the stock at contact $)
pull(sell the stock)
but u need to minus the cost of execute it!!!
eg call warrant u bought $10
can execute to buy the stock @25
market price $40
$40-$25 -$10 =$5 then u gain $5~~~
same case apply to put
understand ??