「上記1~4項までの処理をした後、係る他の案件が生じた場合は」の英訳としては、

If and when any other matter relating hereto not mentioned above should arise after taking the steps in above 1 through 4,

よりも、

After the measures detailed in paragraphs 1 to 4 above have been taken, if and when any other matter relating to the (discontinuation of the agreement) should arise

の方が適切です。