In Article 9: The Parliamentary Parties, insert new Article 9.2 and renumber accordingly:
9.2 Should the post of Leader become vacant before the election of a new Leader, the Deputy Leader of the Parliamentary Party in the House of Commons or, if no such post exists, the Chief Whip of the Parliamentary Party in the House of Commons, shall assume the post of Acting Leader of the Parliamentary Party in the House of Commons until the new Leader is elected.
In Article 10: The Leader, insert new Article 10.6:
10.6 Should the post of Leader become vacant before the election of a new Leader, the Acting Leader of the Parliamentary Party in the House of Commons and the President of the Party shall jointly assume the responsibilities of Leader of the Party until the new Leader is elected.
The existing text of relevant articles of the Federal Constitution:
ARTICLE 9: The Parliamentary Parties
9.1 The Parliamentary Party in the House of Commons shall consist of all Members of that House in receipt of the Party's whip. Its Leader shall be the Leader of the Party elected as provided in Article 10. It shall be entitled to make such regulations (not being inconsistent with this Constitution) as it thinks fit for the conduct of its own proceedings. In particular, these regulations shall make provision for a Chief Whip and, if thought fit, a Deputy Leader of such Parliamentary Party.
ARTICLE 10: The Leader
10.1 The Leader of the Party shall be elected by the members of the Party in accordance with election rules made pursuant to Article 8.4.
10.2 An election for the Leader shall be called upon: (a) the Leader asking for an election; (b) the death or incapacity of the Leader; (c) the Leader ceasing to be a Member of the House of Commons (other than a temporary cessation by reason of a dissolution); (d) the receipt by the President of the resignation of the Leader or of a declaration of intent to resign upon the election of a new Leader; (e) a vote of no confidence in the Leader being passed by a majority of all Members of the Parliamentary Party in the House of Commons; (f) the receipt by the President of a requisition submitted by at least 75 Local Parties (including for this purpose, the Specified Associated Organisation or Organisations representing youth and/or students) following the decision of a quorate general meeting; or (g) the first anniversary of the preceding general election being reached without an election being called under any of paragraphs (a) through (f), provided that: (i) the Federal Executive may postpone such an election for no more than one year by a two-thirds majority of those present and voting; and (ii) this paragraph (g) shall not apply if the Leader is a member of the Government.
10.3 Upon election, the Leader shall hold office until death, incapacity or resignation or the completion of an election called under this Article.
10.4 Upon the calling of an election, the Federal Executive shall publish a timetable for nominations, withdrawals, despatch and receipt of ballot papers and the holding of ballots and shall appoint a disinterested person or body to receive and count the ballot papers.
10.5 Nominations must be of a Member of the Parliamentary Party in the House of Commons, who must be proposed by at least ten percent of other members of the Parliamentary Party in the House of Commons and supported by 200 members in aggregate in not less than 20 Local Parties (including, for this purpose, the Specified Associated Organisations representing youth and students as provided by Article 13.8) and must indicate acceptance of nomination.