Article IV § 3: New States may be admitted by the Congress into this Union; but no new States shall be formed or erected within the Jurisdiction of any other State; nor any State be formed by the Junction of two or more States, or parts of States, without the Consent of the Legislatures of the States concerned as well as of the Congress.
From Madison in Federalist No. 43,
The general precaution that no new States shall be formed without the concurrence of the federal authority and that of the States concerned, is consonant to the principles which ought to govern such transactions. The particular precaution against the erection of new States, by the partition of a State without its consent, quiets the jealousy of the larger States; as that of the smaller is quieted by a like precaution against a junction of States without their consent.
The Constitution is absolutely silent as to the preventing a state from disposal of state lands, the secession of a state, or any other condition outside of the creation of a new state. The only items addressed in this section are the admission/creation of a new state into the union, regardless of where the territory came into possession.
The Constitution is absolutely silent on who specifically can suspend habeas corpus, but that doesn't stop your cohort from stating that since Congess is mentioned in Section 1 then the implication is that Section 9 applies only to Congress as well. Why are implied powers OK there and not OK in Article IV? Other than the fact that one fits your purposes and one does not, of course.
interesting read thanks.