英文中可以用兩個以上的連接詞?

There is a danger, though, that if the individual is ever lucky enough to find what they're looking for, rather than celebrating their success they may feel empty, now that the goal that drove them on has gone.
在上面這個長句裡：
主要子句是：there is a danger（主詞是danger）。
第一個「連接詞」是帶出名詞子句的that: they may feel empty。當作名詞danger的「同位語」。
第二個「連接詞」是帶出副詞子句的if: the individual is every lucky enough to find xxx, rather celebrating their success（給條件：如果...）
第三個「連接詞」是帶出副詞子句的片語now that: the goal ... has gone.（給條件：既然...)
名詞子句what they are looking for當作不定詞to find的受詞。what是「帶先行詞的關係代名詞」。
形容詞子句that drove them on當作名詞goal的修飾語。that是「關係代名詞」。
只要符合語法邏輯，長句裡面可以使用多個連接詞。

There is a danger,though(conjunction =in spite of the fact that),
(1)that(conj., adv. cl.))if the individual is (ever) lucky enough
(2)to find what(rel pron., n.cl on success) they're looking for,
(3)=(4)they may feel empty結果
(4)=(5)既然that(relative pronoun) the goal that(adj.cl.) drove them on has gone目的
(5)=(3)rather than celebrating their success.
Another sample on similar construction of
sentence sample,eg:-
(1) If the poster(=秀秋) is ever(adverb,at any time) lucky enough
(2) to locate the beauty girl neighbor,
(3)you(秀秋) may feel empty
(4)that(rel.pron) all other beauties are lock up
(5)rather than taking them all for your tender LOVE making.

假如你單以連接詞(某字)而言，這類複雜句子complex sentence裏面其實連接表達延續或對比或相反意思的子句時，用連接詞作為轉折和標示是可以的。

其實你指出句中的if並不是跟that連接，而是that後的句前的假設句首詞(全句是)：
if the the individual is ever lucky enough to find what they're looking for, rather than celebrating their success they may feel empty
主要表達「假如他們不能達到想要的目標(what they're looking for)，他們雖然似乎"成功"(success)但仍會感失落(empty)」，當中作者還加入很多"附加"的用語，如此"長氣"以構成他想表達的"複雜"心情。

now that ...是正常的連接詞，只是附加了一點重音now以表達「如今」以對比前句可能是表述一些過往的現像，現在他想說另一狀況。

之後的第二個that drove them on has gone才是另一句才是修飾作者想說明the goal"現在是怎樣跟前文不同。

所以全句裏其實對比兩個主題並在當中寫出"原意目標"跟"結果"的反差，因而你看出當中用了很多"連接"/"轉折"寫法。