Kung sabagay best translates to the adverbs in any case, in that case, or even anyway.
All of the above adverbial phrases (including the Tagalog kung sabagay) aim to explain or expound on a previous statement. In other words, when you use these adverbial phrases, you are saying that the previous statement is true and that you are in fact even adding to the veracity of that statement.
If all you say is "kung sabagay" in response to a statement, it could be correct in the context of an on going conversation because your interlocutor already understands that you agree with him or her and is already cognizant of the reason or other reasons you have in mind for agreeing with him or her. In written form, it would be more properly written as "In any case....", the dots denoting the following statement that is implicit in the ongoing conversation.
Here are some ways your sample text might be completed:
"Shall we drop by the house or go straight to the grocery store? "
"There's no need for us to drop by there anyway."
"Kung sabagay (In any case / Anyway), wala naman tayong kailangan sa bahay / dala ko naman ang pera / mas madali tayong makakabalik kung uunahin natin ang grocery."
If you want to end the conversation with a simple statement, the last sentence could be "Oo nga." or "Tama ka nga."
Ending the conversation with "Kung sabagay..." as I said is acceptable in everyday conversation when both speakers know the implicit statement that follows "kung sabagay..."
Otherwise, kung sabagay by itself (especially in written form) almost seems like a dangling modifier or simply, an incomplete sentence.
there are also other available translations (i think it depends on the context) such as 'oh well', 'as a matter of fact', and others.