should the Party X fail to carry out bla-bla-bla

or
should the Party X failS to carry out bla-bla-bla

второе как-то не то...
но решил проверить , а в английских доках и так, и так))

такие дела.

спасибо, понял.

Ну "икс" - это типа имя стороны какой-либо.

согласен ,тут симпл будет.

но вот личную форму после should, даже в таком значении, я не встречала.

http://www.englisch-hilfen.de/en/grammar/replacing_if.htm

Failing to Pay – Should the Buyer fail to make payment for an agreed contract, without written good reason for a justifiable cause, in accordance with British Law,.....bla-bla-bla...by the Seller to cover these lost discounts occasions by the Buyer’s failure to pay within the agreed period of time. Statements are supplied monthly and failure to inform of missing invoices within 40 days by the Seller necessitates a copy charge by the Vendor of £10.00, Default Letters and Credit Collection phone calls are £10.00 each. Duplicate Invoices are £10.00 at any time.
.....

If at any time the financial condition of Buyer so warrants, or if Buyer fails to make payment(s) when due, or if Buyer fails to supply requested financial documentation, or defaults in any way, ASBIS may either alter terms of payment, suspend credit and delay shipment or pursue any remedies available at law or under this Terms and Conditions of Sale. In such event, ASBIS will be entitled to reimbursement from Buyer for its reasonable expenses, including attorney’s fees.

в том же доке

Should any provision in these Terms and Conditions of Sale be or become invalid, the validity of all other provisions or agreements shall remain unaffected thereby. Buyer and ASBIS shall instead be obliged to replace the invalid provision by a valid one which most effectively serves within the limits allowed by law the economic purpose of the invalid provision.

5.3 Should the Buyer fail to supply components and/or instructions required for the manufacture or finishing of the goods which it has agreed to supply by the date shown overleaf the Seller may suspend delivery until a reasonable time after the supply by the Buyer of the components and/or instructions or it may cancel the agreement without compensation being due from the Seller to the Buyer.

или я в угаре работы юмора не понял)